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/Ruby 2.4

class Binding

Parent:
Object

Objects of class Binding encapsulate the execution context at some particular place in the code and retain this context for future use. The variables, methods, value of self, and possibly an iterator block that can be accessed in this context are all retained. Binding objects can be created using Kernel#binding, and are made available to the callback of Kernel#set_trace_func.

These binding objects can be passed as the second argument of the Kernel#eval method, establishing an environment for the evaluation.

class Demo
  def initialize(n)
    @secret = n
  end
  def get_binding
    binding
  end
end

k1 = Demo.new(99)
b1 = k1.get_binding
k2 = Demo.new(-3)
b2 = k2.get_binding

eval("@secret", b1)   #=> 99
eval("@secret", b2)   #=> -3
eval("@secret")       #=> nil

Binding objects have no class-specific methods.

Public Instance Methods

eval(string [, filename [,lineno]]) → obj Show source

Evaluates the Ruby expression(s) in string, in the binding's context. If the optional filename and lineno parameters are present, they will be used when reporting syntax errors.

def get_binding(param)
  binding
end
b = get_binding("hello")
b.eval("param")   #=> "hello"
static VALUE
bind_eval(int argc, VALUE *argv, VALUE bindval)
{
    VALUE args[4];

    rb_scan_args(argc, argv, "12", &args[0], &args[2], &args[3]);
    args[1] = bindval;
    return rb_f_eval(argc+1, args, Qnil /* self will be searched in eval */);
}
local_variable_defined?(symbol) → obj Show source

Returns true if a local variable symbol exists.

def foo
  a = 1
  binding.local_variable_defined?(:a) #=> true
  binding.local_variable_defined?(:b) #=> false
end

This method is the short version of the following code:

binding.eval("defined?(#{symbol}) == 'local-variable'")
static VALUE
bind_local_variable_defined_p(VALUE bindval, VALUE sym)
{
    ID lid = check_local_id(bindval, &sym);
    const rb_binding_t *bind;

    if (!lid) return Qfalse;

    GetBindingPtr(bindval, bind);
    return get_local_variable_ptr(VM_ENV_ENVVAL_PTR(vm_block_ep(&bind->block)), lid) ? Qtrue : Qfalse;
}
local_variable_get(symbol) → obj Show source

Returns the value of the local variable symbol.

def foo
  a = 1
  binding.local_variable_get(:a) #=> 1
  binding.local_variable_get(:b) #=> NameError
end

This method is the short version of the following code:

binding.eval("#{symbol}")
static VALUE
bind_local_variable_get(VALUE bindval, VALUE sym)
{
    ID lid = check_local_id(bindval, &sym);
    const rb_binding_t *bind;
    const VALUE *ptr;

    if (!lid) goto undefined;

    GetBindingPtr(bindval, bind);

    if ((ptr = get_local_variable_ptr(VM_ENV_ENVVAL_PTR(vm_block_ep(&bind->block)), lid)) == NULL) {
        sym = ID2SYM(lid);
      undefined:
        rb_name_err_raise("local variable `%1$s' not defined for %2$s",
                          bindval, sym);
    }

    return *ptr;
}
local_variable_set(symbol, obj) → obj Show source

Set local variable named symbol as obj.

def foo
  a = 1
  bind = binding
  bind.local_variable_set(:a, 2) # set existing local variable `a'
  bind.local_variable_set(:b, 3) # create new local variable `b'
                                 # `b' exists only in binding

  p bind.local_variable_get(:a)  #=> 2
  p bind.local_variable_get(:b)  #=> 3
  p a                            #=> 2
  p b                            #=> NameError
end

This method behaves similarly to the following code:

binding.eval("#{symbol} = #{obj}")

if obj can be dumped in Ruby code.

static VALUE
bind_local_variable_set(VALUE bindval, VALUE sym, VALUE val)
{
    ID lid = check_local_id(bindval, &sym);
    rb_binding_t *bind;
    const VALUE *ptr;
    const rb_env_t *env;

    if (!lid) lid = rb_intern_str(sym);

    GetBindingPtr(bindval, bind);
    env = VM_ENV_ENVVAL_PTR(vm_block_ep(&bind->block));
    if ((ptr = get_local_variable_ptr(env, lid)) == NULL) {
        /* not found. create new env */
        ptr = rb_binding_add_dynavars(bind, 1, &lid);
        env = VM_ENV_ENVVAL_PTR(vm_block_ep(&bind->block));
    }

    RB_OBJ_WRITE(env, ptr, val);

    return val;
}
local_variables → Array Show source

Returns the names of the binding's local variables as symbols.

def foo
  a = 1
  2.times do |n|
    binding.local_variables #=> [:a, :n]
  end
end

This method is the short version of the following code:

binding.eval("local_variables")
static VALUE
bind_local_variables(VALUE bindval)
{
    const rb_binding_t *bind;
    const rb_env_t *env;

    GetBindingPtr(bindval, bind);
    env = VM_ENV_ENVVAL_PTR(vm_block_ep(&bind->block));
    return rb_vm_env_local_variables(env);
}
receiver → object Show source

Returns the bound receiver of the binding object.

static VALUE
bind_receiver(VALUE bindval)
{
    const rb_binding_t *bind;
    GetBindingPtr(bindval, bind);
    return vm_block_self(&bind->block);
}

Ruby Core © 1993–2017 Yukihiro Matsumoto
Licensed under the Ruby License.
Ruby Standard Library © contributors
Licensed under their own licenses.