I think the escape analysis is at fault here. The two index functions should
have the same characteristics. Both opts.isDigit and the explicit closure
capture the pointer to opts, and I don't see why the compiler shouldn't
be able to detect that the former doesn't escape just as it does the latter.
Please raise an issue at golang.org/issue.
On 4 September 2018 at 19:51, Paul D <pauld...@gmail.com> wrote:
> I'm trying to reduce allocations (and improve performance) in some Go code.
> There's a recurring pattern in the code where a struct is passed to a
> function, and the function passes one of the struct's methods to
> strings.IndexFunc. For some reason, this causes the entire struct to escape
> to the heap. If I wrap the method call in an anonymous function, the struct
> does not escape and the benchmarks run about 30% faster.
>
> Here is a minimal example. In the actual code, the struct has more
> fields/methods and the function in question actually does something. But
> this sample code illustrates the problem. Why does the opts argument escape
> to the heap in index1 but not in the functionally equivalent index2? And is
> there a robust way to ensure that it stays on the stack?
>
>
> type options struct {
> zero rune
> }
>
> func (opts *options) isDigit(r rune) bool {
> r -= opts.zero
> return r >= 0 && r <= 9
> }
>
> // opts escapes to heap
> func index1(s string, opts options) int {
> return strings.IndexFunc(s, opts.isDigit)
> }
>
> // opts does not escape to heap
> func index2(s string, opts options) int {
> return strings.IndexFunc(s, func(r rune) bool {
> return opts.isDigit(r)
> })
> }
>
>
> FYI I'm running Go 1.10.3 on Linux. Thanks...
This seems like
>
>
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