Crystal: Adding type restriction to ivar makes compiler fail

[Jens0512]

Reproducible code:

class Foo
  @bar : Int32 = uninitialized Int32
end

Fails at compile time:

Error in line 2: undefined method 'uninitialized'

While:

class Foo
  @bar = uninitialized Int32
end

Works just as expected, i.e. the programs compiles, and Foo@bar is not initialized.

Crystal version and OS

% crystal -v 
Crystal 0.25.0 (2018-06-12)

LLVM: 6.0.0
Default target: x86_64-pc-linux-gnu

% uname -mors
Linux 4.17.2-1-ARCH x86_64 GNU/Linux

[asterite]

uninitialized is a fixed construct. The only valid syntax is one of these:

name = uninitialized Type
@name = uninitialized Type
@@name = uninitialized Type

That means this is not valid syntax:

@name : Int32 = uninitialized Type

This is not a bug.

I know x = uninitialized Type is not consistent with the rest of the language, but, well, it's not something that should be used, ever. There's always a better solution. It just exists to implement super low-level stuff. In fact, maybe it should be removed from the language altogether and just pay for the small performance hit whenever its used.

[Jens0512]

At least it seems to me that using uninitialized is very practical to use with C bindings and ivars. As long as it is done properly.

I ran into this trying to write some simple getters:

class Foo
  getter bar : Int32 = uninitialized Int32
end

% crystal foo.cr
Error in line 2: expanding macro

in macro 'getter' expanded macro: macro_94066989783344:113, line 4:

   1.       
   2.         
   3.           
>  4.             @bar : Int32 = uninitialized(Int32)
   5. 
   6.             def bar : Int32
   7.               @bar
   8.             end
   9.           
  10.         
  11.       
  12.     

undefined method 'uninitialized'

[straight-shoota]

As long as it is done properly.

Doing it properly means what @asterite said.

What's your issue with that?

@bar = uninitialized Int32
getter bar : Int32

[asterite]

Don't use uninitialized. You really don't need it.

What are you trying to do?

[Jens0512]

Yes. I really don't need it, but I found it to work, hence I use it. There are safer ways, I still use this.

I am not trying to convince you that people should use it, I am trying to tell you:

getter bar : Type = uninitialized Type

fails. Because this only fails when using uninitialized with type restrictions, and getter requires to specify type after ivar name. I think that the current behaviour is not optimal.

[asterite]

I think it is optimal: it's harder for you to use uninitialized variables, and that's a good thing in my opinion.

[ysbaddaden]

Closing. As stated above this is by design. Please use alternatives. Thanks!