Description
Summary
When passing parameters to templates, subsitution may cause the parameter to be evaluated multiple times - warn when this happens
Description
proc f(): int =
echo "hello"
42
template test(a: int): int =
a + a
echo test(f())
In the above template, a is evaluated twice which may be expensive - in the example, "hello" is printed twice which in most cases is both undesirable and inefficient.
In most cases, it's problem with the template declaration: it should probably have captured a in a local variable.
However, this is only a problem when a evaluates to something non-trivial - ie test(425) is not a problem and should not cause an evaluation warning.
Similarly, sometimes the multi-eval is desired, thus there should be a way to disable the warning locally - test(a{.dirty.}: int) would be one option (or some other keyword) - another option would be a call-site annotation.
Alternatives
No response
Examples
No response
Backwards Compatibility
No response
Links
No response