Can and should unconvert simplify this case?

[dmitshur]

Suppose there's a declaration of a []int32 slice done in the following way:

x := []int32{
    (int32)(1),
    (int32)(5),
    (int32)(8),
}

Is there a reason unconvert can't or shouldn't simplify it to:

x := []int32{
    1,
    5,
    8,
}

Since constants are used, the type conversion is not needed, as the constants will have their types inferred correctly from the context. Any thoughts?

[mdempsky]

Nice, I agree the type conversions there are unnecessary because of context, just like in

var x int32 = int32(1)

It should also work the same for struct and map literals.

[dmitshur]

Great!

As I understand, this will only be possible in some cases. For example, if it looks like this:

var x, y, z = 1, 2, 3

s := []int32{
    int32(x),
    int32(y),
    int32(z),
    4,
    5,
}

Then it won't be possible, since variables x, y and z will need to be converted. But if they were declared as int32, then it could be dropped.

It should also work the same for struct and map literals.

Yep. Also arrays. I didn't mention others because I wanted to start the conversation simpler.

[mdempsky]

Correct, in the int32(x) case, x's type is int, so it's a necessary conversion. It's only unnecessary if x is untyped or int32 already.

[dmitshur]

I suspect this issue is also related to https://github.com/mdempsky/unconvert/issues/20#issuecomment-326457163. Specifically, it could be that the reason this case isn't detected and reported because the constants would become untyped as a result.

[mdempsky]

Going to close as a duplicate of #20 since the latter has more details.