Overloading templates using alias

[dlangBugzillaToGithub]

Jesse Phillips reported this on 2014-02-20T21:32:51Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=12216

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Description

When importing a module D allows a modules functions to be brought into the overload set by declaring an alias. Example

-------
import std.ascii;

bool isLower(bool c) {
    return true;
}
alias isLower = std.ascii.isLower;
-------

Templates should allow for the same behavior:

-------
import std.range;
import std.algorithm;
import std.traits;

bool isSorted(alias less = "a < b", Range)(Range r) if (isStaticArray!Arr) {
    return isSorted(r[]);
}
alias isSorted = std.algorithm.isSorted;
-------

[dlangBugzillaToGithub]

greensunny12 commented on 2018-02-10T22:21:22Z

This is going to be tough because some templates are written like this:


foo()
if (a)

foo()
if (!a)


There overloading is rather hard.

However, the following trick should always work:

---
bool isSorted(alias less = "a < b", Range)(Range r)
{
    import std.algorithm : isSortedImpl = isSorted;

    static if (isStaticArray!Range)
    {
        return isSortedImpl!less(r[]);
    }
    else
    {
        return isSortedImpl!less(r[]);
    }
}
---

https://run.dlang.io/is/EL3VEj

Though nowadays this isn't even necessary for isSorted.