Generics, allocation in switch

[Slawomir Pryczek]

Hey guys,

I have a generic function:

func GetParam[T string | int | float64 | json.Number](pp ParsedParams, key string) (T, bool) {
    var zero T
    ...
    switch any(zero).(type) {

It's a simple helper to get a value from a union-like struct. However, I've been told that the any(zero).(type) call causes a heap allocation on every invocation — is that a significant performance concern when the function is called several thousand times per second? Would it be better to replace it with four separate typed functions? Is there some better way?

Thanks

[Axel Wagner]

Pretty sure you've just been misinformed: https://go.dev/play/p/Vl6KGv4Nog7

The compiler knows that you don't do anything with `any(zero)`, so no need to move it to the heap.

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[Jason E. Aten]

Also you can pass special flags to the compiler to see if, under different circumstances, your variables are or are not escaping to the heap. So you don't have to guess what the escape analysis decided. You can check for yourself. For example: go build -gcflags="-m -l" blah.go

https://go.dev/play/p/2mXixib5nzW