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 peformance 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.