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ValueGetter is not supported inmap #886
Description
ValueGetter is not supported inmap:
https://go.dev/play/p/cutaKAgIxHj
package main
import (
"fmt"
"github.com/expr-lang/expr"
"github.com/expr-lang/expr/patcher/value"
"github.com/expr-lang/expr/vm"
)
type customInt struct {
Int int
}
func (v *customInt) AsInt() int {
return v.Int
}
func (v *customInt) AsAny() any {
return v.Int
}
func main() {
env := map[string]any{
"params": map[string]any{
"ValueOne": &customInt{1},
"ValueTwo": &customInt{2},
},
}
program, err := expr.Compile(
"params.ValueOne + params.ValueTwo",
expr.Env(env),
value.ValueGetter,
)
if err != nil {
fmt.Println(err)
return
}
out, err := vm.Run(program, env)
if err != nil {
panic(err)
}
fmt.Println(out)
}The code above produced the following error:
panic: invalid operation: main.customInt + main.customInt (1:17)
| params.ValueOne + params.ValueTwo
| ................^
goroutine 1 [running]:
main.main()
/tmp/sandbox3933238168/prog.go:43 +0x249
Program exited.
In my scenario, it's not possible to define a specific struct. Is there any way to solve this problem?
Activity
antonmedv commentedon Dec 22, 2025
Why do you need to use a value getter?
veezhang commentedon Dec 23, 2025
I have defined a generic type for params, I wang use
params.{key}norparams.{key}.Value()in expr.veezhang commentedon Dec 23, 2025
This isn't the only example; ValueGetter is used in other places as well.
We found that it doesn't work in nested maps, but it works in top-level maps.
antonmedv commentedon Dec 25, 2025
Yes, valuegetter is not part of default expr default behaviour. I regret merging it actually. But why do you need those custom param containers in a first place?
veezhang commentedon Jan 8, 2026
I'm truly sorry for the delay in replying to you.
For example, here I can use the more concise
params.name1andparams.name1.name2instead ofparams.name1.Value(), params.name1.Value().name2.Value().antonmedv commentedon Jan 8, 2026
I see. I will try to look at this issue. But I think another aporoach could be taken.