template: could evalArg/validateType propagate a value of type T to *T, if a method/fn's argument is of type *T? #2235
Description
by mt4swm:
Sometimes one has a struct that contains other structs, or
slices of structs, as members:
type T2 struct {
A T1
B []T1
}
When using the template engine with this struct as data, I
would like to be able to call a Method or a template function
that has an argument of type *T1, not T1, for efficiency.
For now, if a template contains
{{ func .A }}
with func being a user defined function taking one argument
of type *T1, the template engine will print an error like:
template: wrong type for value; expected *T1; got T1
I think it would be nice if the template engine could
automatically take the address of a value, if it detects that
its type then would match a function argument's type.
The patch below to exec.c:validateType tries to implement
this behaviour. It appears to work both in case of methods and functions.
Michael
--- a/src/pkg/template/exec.go
+++ b/src/pkg/template/exec.go
@@ -506,7 +506,11 @@
s.errorf("invalid value; expected %s", typ)
}
if !value.Type().AssignableTo(typ) {
- s.errorf("wrong type for value; expected %s; got %s", typ, value.Type())
+ if reflect.PtrTo(value.Type()).AssignableTo(typ) {
+ value = value.Addr()
+ } else {
+ s.errorf("wrong type for value; expected %s; got %s", typ, value.Type())
+ }
}
return value
}