[Issue 17835] New: std.algorithm.findSplit: Documentation example does not compile

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=17835

          Issue ID: 17835
           Summary: std.algorithm.findSplit: Documentation example does
                    not compile
           Product: D
           Version: D2
          Hardware: x86
                OS: Mac OS X
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: phobos
          Assignee: nobody at puremagic.com
          Reporter: jrdemail2000-dlang at yahoo.com

Documentation for findSplit says:

---------------------------------
Returns:
A sub-type of Tuple!() of the split portions of haystack (see above for
details). This sub-type of Tuple!() has opCast defined for bool. This opCast
returns true when the separating needle was found (!result[1].empty) and false
otherwise. This enables the convenient idiom shown in the following example.

Example
if (const split = haystack.findSplit(needle))
{
     doSomethingWithSplit(split);
}
---------------------------------

However, the example fails to compile with the error message:

Error: mutable method std.algorithm.searching.findSplit!("a == b", string,
string).findSplit.Result!(string, string).Result.opCast!bool.opCast is not
callable using a const object

Changing the example to use 'auto' rather than 'const' works. There is no unit
test of this capability. It does not appear to be a regression, the same error
occurs with DMD 2.072.2 through 2.076.0-dirty.

I didn't try it, but declaring the opCast const (and perhaps pure, nothrow,
@nogc) would make the example work. Otherwise, the documentation should be
change. A unit test would also be appropriate.

This also applies to the sibling functions findSplitBefore and findSplitAfter.

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