Crystal allows declaring uninitialized variables:
x = uninitialized Int32 x # => some random value, garbage, unreliable
This is unsafe code and is almost always used in low-level code for declaring uninitialized StaticArray buffers without a performance penalty:
buffer = uninitialized UInt8[256]
The buffer is allocated on the stack, avoiding a heap allocation.
The type after the uninitialized keyword follows the type grammar.
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https://crystal-lang.org/docs/syntax_and_semantics/declare_var.html