foo.bar - method or key value?

[guamoko995]

Good day everyone!

I might be wrong, but it seems to me that method precedence over keyed value is not documented anywhere. And I'm not even sure if this behavior is stable. Because of this, I don't think foo.bar should be equivalent to foo[bar].

In Go Playground

package main

import (
	"fmt"

	"github.com/expr-lang/expr"
)

type mapWithMethod map[string]func() string

func (m mapWithMethod) GetString() string {
	return "thise is from method"
}

func GetString() string {
	return "thise is from func"
}

type env struct {
	M mapWithMethod
}

func main() {
	env := env{
		M: mapWithMethod{"GetString": GetString},
	}
	prog, _ := expr.Compile(`M.GetString()`, expr.Env(env), expr.Optimize(true))

	result, _ := expr.Run(prog, env)

	fmt.Println(result)
	//Output: thise is from method
}

[antonmedv]

Yes, method usually take precedence. This of this as writing next Go code:

	env := env{
		M: mapWithMethod{"GetString": GetString},
	}

	println(env.M.GetString())

And syntax foo.bar for maps is just syntax sugar.

[guamoko995]

Yes, method usually take precedence. This of this as writing next Go code:

env := env{
M: mapWithMethod{"GetString": GetString},
}

println(env.M.GetString())
And syntax foo.bar for maps is just syntax sugar.

In Go, the syntax allows calling a function retrieved by key. The distinction between accessing a map key ([...]) and a struct method or property using a dot, unlike expr, doesn't allow shadowing (in the case of a struct, it's a compile-time error). Shouldn't shadowing at least be documented? Personally, I think it's wiser to remove this unnecessary syntactic sugar, although it's probably not worth it for backwards compatibility reasons.

package main

import (
	"fmt"
)

type mapWithMethod map[string]func() string

func (m mapWithMethod) Call() string {
	return "from method"
}

func main() {
	v := mapWithMethod{
		"Call": func() string {
			return "from func"
		},
	}

	fmt.Println(v["Call"]())
	fmt.Println(v.Call())

	// Output:
	// from func
	// from method
}

[antonmedv]

Yes, as Expr uses both for acceess as well - calling is limited c