On Tuesday, 13 January 2015 at 07:35:53 UTC, Nordlöw wrote:
Somewhat related to
https://github.com/D-Programming-Language/phobos/pull/2024
I wonder about the soundness of `map` in
```D
import std.algorithm, std.range, std.stdio;
void main(string[] args)
{
long[] arr;
const n = 3;
iota(n).map!(a => arr ~= a);
writeln(arr);
writeln(iota(n).map!(a => arr ~= a));
writeln(arr);
}
```
that prints
```D
[]
[[0], [0, 1], [0, 1, 2]]
[0, 1, 2]
```
Shouldn't a warning at least be issued for return-ignoring calls
to map with mutating lambdas? Has there been any discussions on
making map require pure functions now that we have each? I guess
a new function, say `mapPure`, may be neccessary as adding such
a
restriction to the lambda will break too much code right?
To clarify:
I f() is stronly pure function then DMD since 2.066 will warn
about
f();
, that is, upon return-discarding calls to strongly pure function.
I believe
iota(n).map!(a => arr ~= a);
is a very similar mistake done and if possible should be warned
about.
Is it possible to
- detect that a lambda is has-side-effects and that
- the map hasn't been used?
If this can't (yet) be detected in compiled-time what about
issuing an exception in the destructor of Map to detect this?
Destroy!
