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proposal: spec: expand type inference for short declarations #14326

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dlsniper opened this issue Feb 14, 2016 · 2 comments
Closed

proposal: spec: expand type inference for short declarations #14326

dlsniper opened this issue Feb 14, 2016 · 2 comments
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FrozenDueToAge Proposal v2 A language change or incompatible library change
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Proposal

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@dlsniper
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dlsniper commented Feb 14, 2016 •
edited

Hi,

In the following code:

package main

func main() {
    x := make([]int64, 1000000)
    for i := 0; i < 1000000; i++ {
        x[i] = i
    }
}

the compiler doesn't seem to understand how to set type of i, it gives the following error: : cannot use i (type int) as type int64 in assignment.

I know one can do: x[i] = int64(i) or even better, for i := int64(0); i < 1000000; i++ (the later being a bit better for performance) but in this case I would prefer the Go compiler to optimize this out and not have me manually make the changes needed.

Thank you.
@ianlancetaylor ianlancetaylor changed the title Better type inference in for loops language: better type inference in for loops Feb 14, 2016
@ianlancetaylor ianlancetaylor added the v2 A language change or incompatible library change label Feb 14, 2016
@ianlancetaylor ianlancetaylor added this to the Proposal milestone Feb 14, 2016
@ianlancetaylor
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That would not be a backward compatible change, so it can not happen in Go version 1.

A prerequisite for any such change in any possible Go version 2 would be to write down clear, simple rules for how the type of i is determined.

@rsc rsc changed the title language: better type inference in for loops proposal: spec: expand type inference for short declarations Jun 16, 2017
@ianlancetaylor
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In the absence of clear, simple rules, I am going to close this.

We like type inference but it needs to be clear and straightforward. This approach requires significant analysis, and it's not always clear whether a solution is possible. This sounds more like Haskell than Go.

@golang golang locked and limited conversation to collaborators Jan 9, 2019
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FrozenDueToAge Proposal v2 A language change or incompatible library change
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@dlsniper @ianlancetaylor @gopherbot