Feature Request: Types implementing "fmt.Stringer" should be assignable/comparable to strings
Opened this issue ยท 4 comments
๐ Hello,
I got the following error with this expression: merge_request.state in ["merged", "closed"]
reflect.Value.MapIndex: value of type gitlab.MergeRequestState is not assignable to type string
It would be very nice if types implementing fmt.Stringer
interface to be assignable to strings, or generally treated as strings.
Alternatively, a expr
interface types could implement, making them capable of self-casting to various scalar types.
For reference this is the gitlab.MergeRequestState
type (used in merge_request.state
) implementation
type MergeRequestState string
const (
// All available
MergeRequestStateAll MergeRequestState = "all"
// In closed state
MergeRequestStateClosed MergeRequestState = "closed"
// Discussion has been locked
MergeRequestStateLocked MergeRequestState = "locked"
// Merge request has been merged
MergeRequestStateMerged MergeRequestState = "merged"
// Opened merge request
MergeRequestStateOpened MergeRequestState = "opened"
)
var AllMergeRequestState = []MergeRequestState{
MergeRequestStateAll,
MergeRequestStateClosed,
MergeRequestStateLocked,
MergeRequestStateMerged,
MergeRequestStateOpened,
}
func (e MergeRequestState) IsValid() bool {
switch e {
case MergeRequestStateAll, MergeRequestStateClosed, MergeRequestStateLocked, MergeRequestStateMerged, MergeRequestStateOpened:
return true
}
return false
}
func (e MergeRequestState) String() string {
return string(e)
}
Hello ๐๐ป,
This is a good suggestion. I think it was already proposed multiple times. Although I believe this should not be a default behavior, we can create an official patcher (https://github.com/expr-lang/expr/tree/master/patcher) for fmt.Stringer interface.
This new patcher will automatically add .String()
method calls in these cases:
- All binary nodes:
foo + bar
foo in [x, y, z]
foo matches bar
- Function calls in string params:
func(foo)
- Anything else?
Also let's modify string()
built in to add support for fmt.Stringer interface. We need this as in some caes Expr will bot be able to detect identifer type and users will need to manualy case to string.
Like in next situation, [foo, bar][0]
has any
type.
[foo, bar][0] + "sufix"
There was some similar discussion around this for the ValueGetter
patcher here: #487 (comment)
Off the top of my head time.Duration
and time.Time
both support fmt.Stringer
, so automatic conversion might be unwanted in those cases.
being able to pick fmt.Stringer
or expr.Stringer
(as a ExprString()
interface) would be neat to opt in to behavior and differentiate behaviour if desired :)
@jippi You could take a look at https://pkg.go.dev/github.com/expr-lang/expr@v1.16.7/patcher/value and see if that does what you want (specifically implementing https://pkg.go.dev/github.com/expr-lang/expr@v1.16.7/patcher/value#StringValuer).