I didn't know you can already play around with early access releases of Go2 including generics. This is awsome! I promised myself to start working with Go once it has generics. Therefore, could someone tell me where to download the latest version of Go2 or tell me where the branch of it resides? This is a little off-topic, sorry. But I thought it is not worth creating a new topic just for this lilttle question.
Thank you. Am Samstag, 30. Mai 2020 11:33:37 UTC+2 schrieb Sebastien Binet: > > hi there, > > I was trying out the generics proposal > https://github.com/golang/go/issues/15292, via the "Go2 playground": > https://ccbrown.github.io/wasm-go-playground/experimental/generics > > the thing I am trying to solve is, basically, a generic way to: > - pass a function with any number of parameters and a single return value > - "bind" that function to a slice of pointers to values (that will point > to, e.g., values extracted from a db) > - create a closure that returns the value from evaluating the function > with the bound paramaters. > > basically, I am defining this interface: > type Formula interface { > Vars() []string > Bind(ptrs []interface{}) error > Func() interface{} > } > > that people would be able (in Go-1) to implement like so: > > type FormF64F32ToI64 struct { > vars []string > arg0 *float64 > arg1 *float32 > fct func(x1 float64, x2 float32) int64 > } > > func (f *FormF64F32ToI64) Vars() []string { return f.vars } > func (f *FormF64F32ToI64) Bind(ptrs []interface{}) error { > // check number of args elided. > f.arg0 = ptrs[0].(*float64) > f.arg1 = ptrs[1].(*float32) > return nil > } > > func (f *FormF64F32ToI64) Func() interface{} { > return func() int64 { > return f.fct(*f.arg0, *f.arg1) > } > } > > so some "framework/library" code can work in terms of this Formula > interface and let clients register formulae (with a set of column names to > read from the database) in a relatively type-safe way, and quite performant > one too (you pay the price of the type-assert once when you retrieve the > function closure): > > usr, err := db.Formula(&FormF64F32ToI64{ > names: []string{"col1", "col42"}, > fct: func(x1 float64, x2 float32) int64 { return int64(x1) + int64(x2) > }, > }) > check(err) > > fct := usr.Func().(func () int64) > > err = db.IterRows(func(tx Tx)error { > fmt.Printf("row[%d]: %d\n", tx.ID, fct()) > }) > check(err) > > implementing the Formula interface from a given func is a pretty > mechanical job. > right now, I am doing it with a little go/types-based command. > > today, I tried to do the same with the generics proposal: > > > ===== > package main > > type Formula interface { > Names() []string > Bind(args []interface{}) error > Func() interface{} > } > > type Form2 (type T1,T2,U) struct { > names []string > arg1 *T1 > arg2 *T2 > fct func(t1 T1, t2 T2) U > } > > func (f *Form2(T1,T2,U)) Func() interface{} { > return func() U { > return f.fct(*f.arg1, *f.arg2) > } > } > > func (f *Form2(T1,T2,U)) Names() []string { return f.names } > func (f *Form2(T1,T2,U)) Bind(args []interface{}) error { > if len(args) != 2 { > panic("invalid number of arguments") > } > f.arg1 = args[0].(*T1) > f.arg2 = args[1].(*T2) > return nil > } > > var ( > _ Formula = (*Form2(float64,float32,int64))(nil) > ) > > func main() { > arg1 := 42.0 > arg2 := float32(42) > args := []interface{}{&arg1, &arg2} > > form := &Form2(float64,float32,int64){ > names: []string{"f64", "data"}, > fct: func(x1 float64, x2 float32) int64 { return int64(x1) + > int64(x2) }, > } > err := form.Bind(args) > if err != nil { panic(err) } > > fct := form.Func().(func() int64) > println("fct=",fct()) > } > ==== > > it's definitely an improvement: I "just" have to write the generics code > for functions with a given arity (say, 0, 1, ... 5) w/o having to > pre-generate all the functions I (or my users) may need for all > combinations of (types x arity). > > it's not completely satisfactory, though, as: > - it's not "as general" a solution as what one could come up with, say, > std::function (from C++), where you "just" have to give a function pointer > and it handles everything else for you (arity, in this case) > - there's probably the issue of "generic type argument" collision: > how to differentiate (in the current scheme) between 'func(x1 float64) > (float64, int64)' and 'func(x1, x2 float64) int64'? > (this could perhaps be addressed w/ a different way of describing my > Form2 generic type.) > > perhaps there's a better way of doing this? (perhaps even w/ "just" Go1) > > it'd be great to just have to write: > var f Formula = &Form(func(float64,float64)int64){ > names: names, > fct: func(x1,x2 float64) float32 { return float32(x1+x2) }, > } > and have everything instantiated and implemented correctly. > > thoughts? > > cheers, > -s > > > PS: here's the direct link to the Go+Generics playground of the code > above: > > https://ccbrown.github.io/wasm-go-playground/experimental/generics/#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 > > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. 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