IO::ARGF.new(ARGV, STDIN) An IO for reading files from ARGV.
Usage example:
program.cr:
puts ARGF.gets_to_end
A file to read from: (file)
123
$ crystal build program.cr $ ./program file 123 $ ./program file file 123123 $ # If ARGV is empty, ARGF reads from STDIN instead: $ echo "hello" | ./program hello $ ./program unknown Unhandled exception: Error opening file with mode 'r': 'unknown': No such file or directory (File::NotFoundError) ...
After a file from ARGV has been read, it's removed from ARGV.
You can manipulate ARGV yourself to control what ARGF operates on. If you remove a file from ARGV, it is ignored by ARGF; if you add files to ARGV, ARGF will read from it.
ARGV.replace ["file1"] ARGF.gets_to_end # => Content of file1 ARGV # => [] ARGV << "file2" ARGF.gets_to_end # => Content of file2
Array.new(ARGC_UNSAFE - 1) do |i| String.new(ARGV_UNSAFE[1 + i]) end An array of arguments passed to the program.
{% if flag?(:windows) %}
"\r\n"
{% else %}
"\n"
{% end %} The newline constant
String.new(ARGV_UNSAFE.value) The name, the program was called with.
The result may be a relative or absolute path (including symbolic links), just the command name or the empty string.
See Process.executable_path for a more convenient alternative that always returns the absolute real path to the executable file (if it exists).
IO::FileDescriptor.from_stdio(2) The standard error file descriptor.
Typically used to output error messages and diagnostics.
At the start of the program STDERR is configured like this:
sync is true, meaning that output will be outputted as soon as it is written to STDERR. This is so users can see real time output data.sync is false but flush_on_newline is true. This is so that if you pipe the output to a file, and, for example, you tail -f, you can see data on a line-per-line basis. This is convenient but slower than with flush_on_newline set to false. If you need a bit more performance and you don't care about near real-time output you can do STDERR.flush_on_newline = false.On Unix systems, if the file descriptor is a TTY, the runtime duplicates it. So STDERR.fd might not be 2. The reason for this is to enable non-blocking writes for concurrency. Other fibers can run while waiting on IO. The original file descriptor is inherited from the parent process. Setting it to non-blocking mode would reflect back which can cause problems.
On Windows, STDERR is always blocking.
IO::FileDescriptor.from_stdio(0) The standard input file descriptor. Contains data piped to the program.
On Unix systems, if the file descriptor is a TTY, the runtime duplicates it. So STDIN.fd might not be 0. The reason for this is to enable non-blocking reads for concurrency. Other fibers can run while waiting on user input. The original file descriptor is inherited from the parent process. Setting it to non-blocking mode would reflect back, which can cause problems.
On Windows, STDIN is always blocking.
IO::FileDescriptor.from_stdio(1) The standard output file descriptor.
Typically used to output data and information.
At the start of the program STDOUT is configured like this:
sync is true, meaning that output will be outputted as soon as it is written to STDOUT. This is so users can see real time output data.sync is false but flush_on_newline is true. This is so that if you pipe the output to a file, and, for example, you tail -f, you can see data on a line-per-line basis. This is convenient but slower than with flush_on_newline set to false. If you need a bit more performance and you don't care about near real-time output you can do STDOUT.flush_on_newline = false.On Unix systems, if the file descriptor is a TTY, the runtime duplicates it. So STDOUT.fd might not be 1. The reason for this is to enable non-blocking writes for concurrency. Other fibers can run while waiting on IO. The original file descriptor is inherited from the parent process. Setting it to non-blocking mode would reflect back which can cause problems.
On Windows, STDOUT is always blocking.
Returns the standard output of executing command in a subshell.
Terminates execution immediately, printing message to STDERR and then calling exit(status).
Returns the alignment of the given type as number of bytes.
Registers the given Proc for execution when the program exits regularly.
Returns the current execution stack as an array containing strings usually in the form file:line:column or file:line:column in 'method'.
Terminates execution immediately, returning the given status code to the invoking environment.
Reads a line from STDIN.
Returns the instance alignment of the given class as number of bytes.
Returns the instance size of the given class as number of bytes.
Repeatedly executes the block.
Main function that acts as C's main function.
Returns the byte offset of an instance variable in a struct or class type.
Inspects object to STDOUT followed by a newline.
Inspects each object in objects to STDOUT, followed by a newline.
Inspects objects to STDOUT, followed by a newline.
Returns a Pointer to the contents of a variable.
Pretty prints object to STDOUT followed by a newline.
Pretty prints each object in objects to STDOUT, followed by a newline.
Pretty prints objects to STDOUT, followed by a newline.
Prints objects to STDOUT and then invokes STDOUT.flush.
Prints a formatted string to STDOUT.
Prints a formatted string to STDOUT.
Raises the exception.
Raises an Exception with the message.
See Random#rand(x).
See Random#rand.
Reads a line from STDIN.
Returns the size of the given type as number of bytes.
Blocks the current fiber for the specified number of seconds.
DEPRECATED Use ::sleep(Time::Span) instead
Blocks the current Fiber for the specified time span.
Blocks the current fiber forever.
Spawns a new fiber.
Returns a formatted string.
Returns a formatted string.
Executes the given command in a subshell.
Timeout keyword for use in select.
Returns the type of an expression.
Invokes an execution trap to catch the attention of a debugger.
Prints a series of expressions together with their inspected values.
Prints a series of expressions together with their pretty printed values.
Defines a Struct type called name with the given properties.
Spec::Methods
Spec::Methods
Spec::Expectations
Spec::Expectations
Returns the standard output of executing command in a subshell. Standard input, and error are inherited. The special $? variable is set to a Process::Status associated with this execution.
It is impossible to call this method with any regular call syntax. There is an associated literal type which calls the method with the literal content as command:
`echo hi` # => "hi\n" $?.success? # => true
See Command literals in the language reference.
Terminates execution immediately, printing message to STDERR and then calling exit(status).
Returns the alignment of the given type as number of bytes.
type must be a constant or typeof() expression. It cannot be evaluated at runtime.
alignof(Int32) # => 4 alignof(Float64) # usually 4 or 8 alignof(typeof(true)) # => 1
For Reference types, the alignment is the same as the alignment of a pointer:
# On a 64 bits machine alignof(Pointer(Int32)) # => 8 alignof(String) # => 8
This is because a Reference's memory is allocated on the heap and a pointer to it is passed around. The alignment of a class on the heap can be determined using #instance_alignof.
alignof in the language specification.NOTE This is a pseudo-method provided directly by the Crystal compiler. It cannot be redefined nor overridden.
Registers the given Proc for execution when the program exits regularly.
A regular exit happens when either
::exit is called.Process.exit does not trigger at_exit handlers, nor does external process termination (see Process.on_terminate for handling that).
If multiple handlers are registered, they are executed in reverse order of registration.
def do_at_exit(str1)
at_exit { print str1 }
end
at_exit { puts "cruel world" }
do_at_exit("goodbye ")
exit Produces:
goodbye cruel world
The exit status code that will be returned by this program is passed to the block as its first argument. In case of any unhandled exception, it is passed as the second argument to the block, if the program terminates normally or exit(status) is called explicitly, then the second argument will be nil.
NOTE If at_exit is called inside an at_exit handler, it will be called right after the current at_exit handler ends, and then other handlers will be invoked.
Returns the current execution stack as an array containing strings usually in the form file:line:column or file:line:column in 'method'.
Terminates execution immediately, returning the given status code to the invoking environment.
Registered at_exit procs are executed.
Returns the instance alignment of the given class as number of bytes.
type must be a constant or typeof() expression. It cannot be evaluated at runtime.
instance_alignof(String) # => 4 instance_alignof(Exception) # => 8
See alignof for determining the size of value types.
instance_alignof in the language specification.NOTE This is a pseudo-method provided directly by the Crystal compiler. It cannot be redefined nor overridden.
Returns the instance size of the given class as number of bytes.
type must be a constant or typeof() expression. It cannot be evaluated at runtime.
instance_sizeof(String) # => 16 instance_sizeof(Exception) # => 48
See sizeof for determining the size of value types.
instance_sizeof in the language specification.NOTE This is a pseudo-method provided directly by the Crystal compiler. It cannot be redefined nor overridden.
Repeatedly executes the block.
loop do line = gets break unless line # ... end
Main function that acts as C's main function. Invokes Crystal.main.
Can be redefined. See Crystal.main for examples.
On Windows the actual entry point is wmain, but there is no need to redefine that. See the file required below for details.
Returns the byte offset of an instance variable in a struct or class type.
type must be a constant or typeof() expression. It cannot be evaluated at runtime. offset must be the name of an instance variable of type, prefixed by @, or the index of an element in a Tuple, starting from 0, if type is a Tuple.
offsetof(String, @bytesize) # => 4
offsetof(Exception, @message) # => 8
offsetof(Time, @location) # => 16
offsetof({Int32, Int8, Int32}, 0) # => 0
offsetof({Int32, Int8, Int32}, 1) # => 4
offsetof({Int32, Int8, Int32}, 2) # => 8 offsetof in the language specification.NOTE This is a pseudo-method provided directly by the Crystal compiler. It cannot be redefined nor overridden.
Inspects object to STDOUT followed by a newline. Returns object.
See also: Object#inspect(io).
Inspects each object in objects to STDOUT, followed by a newline. Returns objects.
See also: Object#inspect(io).
Inspects objects to STDOUT, followed by a newline. Returns objects.
p foo: 23, bar: 42 # => {foo: 23, bar: 42} See Object#inspect(io)
Returns a Pointer to the contents of a variable.
variable must be a variable (local, instance, class or library).
a = 1 ptr = pointerof(a) ptr.value = 2 a # => 2
pointerof in the language specification.NOTE This is a pseudo-method provided directly by the Crystal compiler. It cannot be redefined nor overridden.
Pretty prints object to STDOUT followed by a newline. Returns object.
See also: Object#pretty_print(pp).
Pretty prints each object in objects to STDOUT, followed by a newline. Returns objects.
See also: Object#pretty_print(pp).
Pretty prints objects to STDOUT, followed by a newline. Returns objects.
p foo: 23, bar: 42 # => {foo: 23, bar: 42} See Object#pretty_print(pp)
Prints objects to STDOUT and then invokes STDOUT.flush.
See also: IO#print.
Raises the exception.
This will set the exception's callstack if it hasn't been already. Re-raising a previously caught exception won't replace the callstack.
See Random#rand(x).
Returns the size of the given type as number of bytes.
type must be a constant or typeof() expression. It cannot be evaluated at runtime.
sizeof(Int32) # => 4 sizeof(Int64) # => 8 sizeof(typeof(true)) # => 1
For Reference types, the size is the same as the size of a pointer:
# On a 64 bits machine sizeof(Pointer(Int32)) # => 8 sizeof(String) # => 8
This is because a Reference's memory is allocated on the heap and a pointer to it is passed around. The size of a class on the heap can be determined using #instance_sizeof.
sizeof in the language specification.NOTE This is a pseudo-method provided directly by the Crystal compiler. It cannot be redefined nor overridden.
Blocks the current fiber for the specified number of seconds.
While this fiber is waiting this time, other ready-to-execute fibers might start their execution.
DEPRECATED Use ::sleep(Time::Span) instead
Blocks the current Fiber for the specified time span.
While this fiber is waiting this time, other ready-to-execute fibers might start their execution.
Blocks the current fiber forever.
Meanwhile, other ready-to-execute fibers might start their execution.
Spawns a new fiber.
When using execution contexts, the fiber spawns into the current execution context (Fiber::ExecutionContext.current).
NOTE The newly created fiber doesn't run as soon as spawned.
Example:
# Write "1" every 1 second and "2" every 2 seconds for 6 seconds.
require "wait_group"
wg = WaitGroup.new 2
spawn do
6.times do
sleep 1.second
puts 1
end
ensure
wg.done
end
spawn do
3.times do
sleep 2.seconds
puts 2
end
ensure
wg.done
end
wg.wait Returns a formatted string. The string is produced according to the format_string with format specifiers being replaced by values from args formatted according to the specifier.
Within the format string, any characters other than format specifiers (specifiers beginning with %) are copied to the result. The formatter supports the following kinds of format specifiers:
%.1f). The first % consumes the first argument, the second consumes the second argument, and so on.%3$.1f). The one-based argument index is specified as part of the flags.%<name>.1f, %{name}). The angle bracket form accepts flags and the curly bracket form doesn't. Exactly one Hash or NamedTuple must be passed as the argument.Mixing of different kinds of format specifiers is disallowed, except that the two named forms may be used together.
A simple format specifier consists of a percent sign, followed by optional flags, width, and precision indicators, then terminated with a field type character.
%[flags][width][.precision]type
A formatted substitution is similar but after the percent sign follows the mandatory name of the substitution wrapped in angle brackets.
%<name>[flags][width][.precision]type
The percent sign itself is escaped by %%. No format modifiers are allowed, and no arguments are consumed.
The field type controls how the corresponding argument value is to be interpreted, while the flags modify that interpretation.
The field type characters are:
Field | Integer Format
------+------------------------------------------------------------------
b | Formats argument as a binary number.
d | Formats argument as a decimal number.
i | Same as d.
o | Formats argument as an octal number.
x | Formats argument as a hexadecimal number using lowercase letters.
X | Same as x, but uses uppercase letters.
Field | Float Format
------+---------------------------------------------------------------
e | Formats floating point argument into exponential notation
| with one digit before the decimal point as [-]d.dddddde[+-]dd.
| The precision specifies the number of digits after the decimal
| point (defaulting to six).
E | Equivalent to e, but uses an uppercase E to indicate
| the exponent.
f | Formats floating point argument as [-]ddd.dddddd,
| where the precision specifies the number of digits after
| the decimal point.
g | Formats a floating point number using exponential form
| if the exponent is less than -4 or greater than or
| equal to the precision, or in dd.dddd form otherwise.
| The precision specifies the number of significant digits.
G | Equivalent to g, but use an uppercase E in exponent form.
a | Formats floating point argument as [-]0xh.hhhhp[+-]dd,
| which consists of an optional sign, "0x", fraction part
| as hexadecimal, "p", and exponential part as decimal.
A | Equivalent to a, but uses uppercase X and P.
Field | Other Format
------+------------------------------------------------------------
c | Argument is a single character itself.
s | Argument is a string to be substituted. If the format
| sequence contains a precision, at most that many characters
| will be copied. Flags modify the behavior of the format specifiers:
Flag | Applies to | Meaning
---------+---------------+----------------------------------------------------
space | bdiouxX | Add a leading space character to
| aAeEfgG | non-negative numbers. Has no effect if the plus
| (numeric fmt) | flag is also given.
---------+---------------+----------------------------------------------------
# | boxX | Use an alternative format.
| aAeEfgG | For x, X, b, prefix any non-zero result with
| | 0x, 0X, or 0b respectively.
| | For o, prefix any non-zero result with 0o. Note
| | that this prefix is different from C and Ruby.
| | For a, A, e, E, f, g, G,
| | force a decimal point to be added,
| | even if no digits follow.
| | For g and G, do not remove trailing zeros.
---------+---------------+----------------------------------------------------
+ | bdiouxX | Add a leading plus sign to non-negative
| aAeEfgG | numbers.
| (numeric fmt) |
---------+---------------+----------------------------------------------------
- | all | Left-justify the result of this conversion.
---------+---------------+----------------------------------------------------
0 (zero) | bdiouxX | Pad with zeros, not spaces. Has no effect if the
| aAeEfgG | number is left-justified, or a precision is given
| (numeric fmt) | to an integer field type.
---------+---------------+----------------------------------------------------
* | all | Use the next argument as the field width or
| | precision. If width is negative, set the minus flag
| | and use the argument's absolute value as field
| | width. If precision is negative, it is ignored.
---------+---------------+----------------------------------------------------
1$ 2$ 3$ | all | As a flag, specifies the one-based argument index
... | | for a positional format specifier.
| | Immediately after *, use the argument at the given
| | one-based index as the width or precision, instead
| | of the next argument. The entire format string must
| | also use positional format specifiers throughout. Examples of flags:
Decimal number conversion:
sprintf "%d", 123 # => "123" sprintf "%+d", 123 # => "+123" sprintf "% d", 123 # => " 123"
Octal number conversion:
sprintf "%o", 123 # => "173" sprintf "%+o", 123 # => "+173" sprintf "%o", -123 # => "-173" sprintf "%+o", -123 # => "-173"
Hexadecimal number conversion:
sprintf "%x", 123 # => "7b" sprintf "%+x", 123 # => "+7b" sprintf "%x", -123 # => "-7b" sprintf "%+x", -123 # => "-7b" sprintf "%#x", 0 # => "0" sprintf "% x", 123 # => " 7b" sprintf "% x", -123 # => "-7b" sprintf "%X", 123 # => "7B" sprintf "%#X", -123 # => "-0X7B"
Binary number conversion:
sprintf "%b", 123 # => "1111011" sprintf "%+b", 123 # => "+1111011" sprintf "%+b", -123 # => "-1111011" sprintf "%b", -123 # => "-1111011" sprintf "%#b", 0 # => "0" sprintf "% b", 123 # => " 1111011" sprintf "%+ b", 123 # => "+1111011" sprintf "% b", -123 # => "-1111011" sprintf "%+ b", -123 # => "-1111011" sprintf "%#b", 123 # => "0b1111011"
Floating point conversion:
sprintf "%a", 123 # => "0x1.ecp+6" sprintf "%A", 123 # => "0X1.ECP+6"
Exponential form conversion:
sprintf "%g", 123.4 # => "123.4" sprintf "%g", 123.4567 # => "123.457" sprintf "%20.8g", 1234.56789 # => " 1234.5679" sprintf "%20.8g", 123456789 # => " 1.2345679e+08" sprintf "%20.8G", 123456789 # => " 1.2345679E+08" sprintf "%20.8g", -123456789 # => " -1.2345679e+08" sprintf "%20.8G", -123456789 # => " -1.2345679E+08"
The field width is an optional integer, followed optionally by a period and a precision. The width specifies the minimum number of characters that will be written to the result for this field.
Examples of width:
sprintf "%20d", 123 # => " 123" sprintf "%+20d", 123 # => " +123" sprintf "%020d", 123 # => "00000000000000000123" sprintf "%+020d", 123 # => "+0000000000000000123" sprintf "% 020d", 123 # => " 0000000000000000123" sprintf "%-20d", 123 # => "123 " sprintf "%-+20d", 123 # => "+123 " sprintf "%- 20d", 123 # => " 123 " sprintf "%020x", -123 # => "-000000000000000007b" sprintf "%020X", -123 # => "-000000000000000007B"
For numeric fields, the precision controls the number of decimal places displayed.
For string fields, the precision determines the maximum number of characters to be copied from the string.
Examples of precisions:
Precision for d, o, x and b is minimum number of digits:
sprintf "%20.8d", 123 # => " 00000123" sprintf "%020.8d", 123 # => " 00000123" sprintf "%20.8o", 123 # => " 00000173" sprintf "%020.8o", 123 # => " 00000173" sprintf "%20.8x", 123 # => " 0000007b" sprintf "%020.8x", 123 # => " 0000007b" sprintf "%20.8b", 123 # => " 01111011" sprintf "%20.8d", -123 # => " -00000123" sprintf "%020.8d", -123 # => " -00000123" sprintf "%20.8o", -123 # => " -00000173" sprintf "%20.8x", -123 # => " -0000007b" sprintf "%20.8b", -11 # => " -00001011"
Precision for e is number of digits after the decimal point:
sprintf "%20.8e", 1234.56789 # => " 1.23456789e+03"
Precision for f is number of digits after the decimal point:
sprintf "%20.8f", 1234.56789 # => " 1234.56789000"
Precision for g is number of significant digits:
sprintf "%20.8g", 1234.56789 # => " 1234.5679" sprintf "%20.8g", 123456789 # => " 1.2345679e+08" sprintf "%-20.8g", 123456789 # => "1.2345679e+08 "
Precision for s is maximum number of characters:
sprintf "%20.8s", "string test" # => " string t"
Additional examples:
sprintf "%d %04x", 123, 123 # => "123 007b" sprintf "%08b '%4s'", 123, 123 # => "01111011 ' 123'" sprintf "%+g:% g:%-g", 1.23, 1.23, 1.23 # => "+1.23: 1.23:1.23" sprintf "%-3$*1$.*2$s", 10, 5, "abcdefghij" # => "abcde "
Returns a formatted string. The string is produced according to the format_string with format specifiers being replaced by values from args formatted according to the specifier.
Within the format string, any characters other than format specifiers (specifiers beginning with %) are copied to the result. The formatter supports the following kinds of format specifiers:
%.1f). The first % consumes the first argument, the second consumes the second argument, and so on.%3$.1f). The one-based argument index is specified as part of the flags.%<name>.1f, %{name}). The angle bracket form accepts flags and the curly bracket form doesn't. Exactly one Hash or NamedTuple must be passed as the argument.Mixing of different kinds of format specifiers is disallowed, except that the two named forms may be used together.
A simple format specifier consists of a percent sign, followed by optional flags, width, and precision indicators, then terminated with a field type character.
%[flags][width][.precision]type
A formatted substitution is similar but after the percent sign follows the mandatory name of the substitution wrapped in angle brackets.
%<name>[flags][width][.precision]type
The percent sign itself is escaped by %%. No format modifiers are allowed, and no arguments are consumed.
The field type controls how the corresponding argument value is to be interpreted, while the flags modify that interpretation.
The field type characters are:
Field | Integer Format
------+------------------------------------------------------------------
b | Formats argument as a binary number.
d | Formats argument as a decimal number.
i | Same as d.
o | Formats argument as an octal number.
x | Formats argument as a hexadecimal number using lowercase letters.
X | Same as x, but uses uppercase letters.
Field | Float Format
------+---------------------------------------------------------------
e | Formats floating point argument into exponential notation
| with one digit before the decimal point as [-]d.dddddde[+-]dd.
| The precision specifies the number of digits after the decimal
| point (defaulting to six).
E | Equivalent to e, but uses an uppercase E to indicate
| the exponent.
f | Formats floating point argument as [-]ddd.dddddd,
| where the precision specifies the number of digits after
| the decimal point.
g | Formats a floating point number using exponential form
| if the exponent is less than -4 or greater than or
| equal to the precision, or in dd.dddd form otherwise.
| The precision specifies the number of significant digits.
G | Equivalent to g, but use an uppercase E in exponent form.
a | Formats floating point argument as [-]0xh.hhhhp[+-]dd,
| which consists of an optional sign, "0x", fraction part
| as hexadecimal, "p", and exponential part as decimal.
A | Equivalent to a, but uses uppercase X and P.
Field | Other Format
------+------------------------------------------------------------
c | Argument is a single character itself.
s | Argument is a string to be substituted. If the format
| sequence contains a precision, at most that many characters
| will be copied. Flags modify the behavior of the format specifiers:
Flag | Applies to | Meaning
---------+---------------+----------------------------------------------------
space | bdiouxX | Add a leading space character to
| aAeEfgG | non-negative numbers. Has no effect if the plus
| (numeric fmt) | flag is also given.
---------+---------------+----------------------------------------------------
# | boxX | Use an alternative format.
| aAeEfgG | For x, X, b, prefix any non-zero result with
| | 0x, 0X, or 0b respectively.
| | For o, prefix any non-zero result with 0o. Note
| | that this prefix is different from C and Ruby.
| | For a, A, e, E, f, g, G,
| | force a decimal point to be added,
| | even if no digits follow.
| | For g and G, do not remove trailing zeros.
---------+---------------+----------------------------------------------------
+ | bdiouxX | Add a leading plus sign to non-negative
| aAeEfgG | numbers.
| (numeric fmt) |
---------+---------------+----------------------------------------------------
- | all | Left-justify the result of this conversion.
---------+---------------+----------------------------------------------------
0 (zero) | bdiouxX | Pad with zeros, not spaces. Has no effect if the
| aAeEfgG | number is left-justified, or a precision is given
| (numeric fmt) | to an integer field type.
---------+---------------+----------------------------------------------------
* | all | Use the next argument as the field width or
| | precision. If width is negative, set the minus flag
| | and use the argument's absolute value as field
| | width. If precision is negative, it is ignored.
---------+---------------+----------------------------------------------------
1$ 2$ 3$ | all | As a flag, specifies the one-based argument index
... | | for a positional format specifier.
| | Immediately after *, use the argument at the given
| | one-based index as the width or precision, instead
| | of the next argument. The entire format string must
| | also use positional format specifiers throughout. Examples of flags:
Decimal number conversion:
sprintf "%d", 123 # => "123" sprintf "%+d", 123 # => "+123" sprintf "% d", 123 # => " 123"
Octal number conversion:
sprintf "%o", 123 # => "173" sprintf "%+o", 123 # => "+173" sprintf "%o", -123 # => "-173" sprintf "%+o", -123 # => "-173"
Hexadecimal number conversion:
sprintf "%x", 123 # => "7b" sprintf "%+x", 123 # => "+7b" sprintf "%x", -123 # => "-7b" sprintf "%+x", -123 # => "-7b" sprintf "%#x", 0 # => "0" sprintf "% x", 123 # => " 7b" sprintf "% x", -123 # => "-7b" sprintf "%X", 123 # => "7B" sprintf "%#X", -123 # => "-0X7B"
Binary number conversion:
sprintf "%b", 123 # => "1111011" sprintf "%+b", 123 # => "+1111011" sprintf "%+b", -123 # => "-1111011" sprintf "%b", -123 # => "-1111011" sprintf "%#b", 0 # => "0" sprintf "% b", 123 # => " 1111011" sprintf "%+ b", 123 # => "+1111011" sprintf "% b", -123 # => "-1111011" sprintf "%+ b", -123 # => "-1111011" sprintf "%#b", 123 # => "0b1111011"
Floating point conversion:
sprintf "%a", 123 # => "0x1.ecp+6" sprintf "%A", 123 # => "0X1.ECP+6"
Exponential form conversion:
sprintf "%g", 123.4 # => "123.4" sprintf "%g", 123.4567 # => "123.457" sprintf "%20.8g", 1234.56789 # => " 1234.5679" sprintf "%20.8g", 123456789 # => " 1.2345679e+08" sprintf "%20.8G", 123456789 # => " 1.2345679E+08" sprintf "%20.8g", -123456789 # => " -1.2345679e+08" sprintf "%20.8G", -123456789 # => " -1.2345679E+08"
The field width is an optional integer, followed optionally by a period and a precision. The width specifies the minimum number of characters that will be written to the result for this field.
Examples of width:
sprintf "%20d", 123 # => " 123" sprintf "%+20d", 123 # => " +123" sprintf "%020d", 123 # => "00000000000000000123" sprintf "%+020d", 123 # => "+0000000000000000123" sprintf "% 020d", 123 # => " 0000000000000000123" sprintf "%-20d", 123 # => "123 " sprintf "%-+20d", 123 # => "+123 " sprintf "%- 20d", 123 # => " 123 " sprintf "%020x", -123 # => "-000000000000000007b" sprintf "%020X", -123 # => "-000000000000000007B"
For numeric fields, the precision controls the number of decimal places displayed.
For string fields, the precision determines the maximum number of characters to be copied from the string.
Examples of precisions:
Precision for d, o, x and b is minimum number of digits:
sprintf "%20.8d", 123 # => " 00000123" sprintf "%020.8d", 123 # => " 00000123" sprintf "%20.8o", 123 # => " 00000173" sprintf "%020.8o", 123 # => " 00000173" sprintf "%20.8x", 123 # => " 0000007b" sprintf "%020.8x", 123 # => " 0000007b" sprintf "%20.8b", 123 # => " 01111011" sprintf "%20.8d", -123 # => " -00000123" sprintf "%020.8d", -123 # => " -00000123" sprintf "%20.8o", -123 # => " -00000173" sprintf "%20.8x", -123 # => " -0000007b" sprintf "%20.8b", -11 # => " -00001011"
Precision for e is number of digits after the decimal point:
sprintf "%20.8e", 1234.56789 # => " 1.23456789e+03"
Precision for f is number of digits after the decimal point:
sprintf "%20.8f", 1234.56789 # => " 1234.56789000"
Precision for g is number of significant digits:
sprintf "%20.8g", 1234.56789 # => " 1234.5679" sprintf "%20.8g", 123456789 # => " 1.2345679e+08" sprintf "%-20.8g", 123456789 # => "1.2345679e+08 "
Precision for s is maximum number of characters:
sprintf "%20.8s", "string test" # => " string t"
Additional examples:
sprintf "%d %04x", 123, 123 # => "123 007b" sprintf "%08b '%4s'", 123, 123 # => "01111011 ' 123'" sprintf "%+g:% g:%-g", 1.23, 1.23, 1.23 # => "+1.23: 1.23:1.23" sprintf "%-3$*1$.*2$s", 10, 5, "abcdefghij" # => "abcde "
Executes the given command in a subshell. Standard input, output and error are inherited. Returns true if the command gives zero exit code, false otherwise. The special $? variable is set to a Process::Status associated with this execution.
If command contains no spaces and args is given, it will become its argument list.
If command contains spaces and args is given, command must include "${@}" (including the quotes) to receive the argument list.
No shell interpretation is done in args.
Example:
system("echo *") Produces:
LICENSE shard.yml Readme.md spec src
Timeout keyword for use in select.
select
when x = ch.receive
puts "got #{x}"
when timeout(1.seconds)
puts "timeout"
end NOTE It won't trigger if the select has an else case (i.e.: a non-blocking select).
Returns the type of an expression.
typeof(1) # => Int32
It accepts multiple arguments, and the result is the union of the expression types:
typeof(1, "a", 'a') # => (Int32 | String | Char)
The expressions passed as arguments to typeof do not evaluate. The compiler only analyzes their return type.
typeof in the language specification.NOTE This is a pseudo-method provided directly by the Crystal compiler. It cannot be redefined nor overridden.
Invokes an execution trap to catch the attention of a debugger. This has the same effect as placing a breakpoint in debuggers or IDEs supporting them.
Execution is allowed to continue if the debugger instructs so. If no debugger is attached, usually the current process terminates with a status that corresponds to Process::ExitReason::Breakpoint.
Inside an interpreter session, this drops into the REPL's pry mode instead of a system debugger.
Prints a series of expressions together with their inspected values. Useful for print style debugging.
a = 1 p! a # => "a # => 1" p! [1, 2, 3].map(&.to_s) # => "[1, 2, 3].map(&.to_s) # => ["1", "2", "3"]"
See also: p, Object#inspect.
Prints a series of expressions together with their pretty printed values. Useful for print style debugging.
a = 1 pp! a # => "a # => 1" pp! [1, 2, 3].map(&.to_s) # => "[1, 2, 3].map(&.to_s) # => ["1", "2", "3"]"
See also: pp, Object#pretty_inspect.
Defines a Struct type called name with the given properties.
The generated struct has a constructor with the given properties in the same order as declared. The struct only provides getters, not setters, making it immutable by default.
record Point, x : Int32, y : Int32 p = Point.new 1, 2 # => #<Point(@x=1, @y=2)> p.x # => 1 p.y # => 2
The properties are a sequence of type declarations (x : Int32, x : Int32 = 0) or assigns (x = 0). They declare instance variables and respective getter methods of their name with optional type restrictions and default value.
When passing a block to this macro its body is inserted inside the struct definition. This allows to define additional methods or include modules into the record type (reopening the type would work as well).
record Person, first_name : String, last_name : String do
def full_name
"#{first_name} #{last_name}"
end
end
person = Person.new "John", "Doe"
person.full_name # => "John Doe" An example with type declarations and default values:
record Point, x : Int32 = 0, y : Int32 = 0 Point.new # => #<Point(@x=0, @y=0)> Point.new y: 2 # => #<Point(@x=0, @y=2)>
An example with assignments (in this case the compiler must be able to infer the types from the default values):
record Point, x = 0, y = 0 Point.new # => #<Point(@x=0, @y=0)> Point.new y: 2 # => #<Point(@x=0, @y=2)>
This macro also provides a #copy_with method which returns a copy of the record with the provided properties altered.
record Point, x = 0, y = 0 p = Point.new y: 2 # => #<Point(@x=0, @y=2)> p.copy_with x: 3 # => #<Point(@x=3, @y=2)> p # => #<Point(@x=0, @y=2)>
Spawns a fiber by first creating a Proc, passing the call's expressions to it, and letting the Proc finally invoke the call.
When using execution contexts, the fiber spawns into the current execution context (Fiber::ExecutionContext.current).
Compare this:
i = 0
while i < 5
spawn { print(i) }
i += 1
end
Fiber.yield
# Output: 55555 To this:
i = 0 while i < 5 spawn print(i) i += 1 end Fiber.yield # Output: 01234
This is because in the first case all spawned fibers refer to the same local variable, while in the second example copies of i are passed to a Proc that eventually invokes the call.
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Licensed under the Apache License, Version 2.0.
https://crystal-lang.org/api/1.19.0/toplevel.html