SplitIterator panics when doing SplitIterator.first() twice

[sfiedler0]

Zig Version

0.14.0-dev.2569+30169d1d2

Steps to Reproduce and Observed Behavior

1. Write some code that uses the SplitIterator (std.mem.splitAny)
2. Call twice your split_iterator.first()
3. Observe a panic: reached unreachable code after calling the second split_iterator.first()

Example code:

const std = @import("std");

test "this will crash" {
    var split_iterator = std.mem.splitAny(u8, "test|test|test", "|");
    std.debug.print("{s}\n", .{ split_iterator.first() });
    std.debug.print("{s}\n", .{ split_iterator.first() });
}

Expected Behavior

I expected that function to either succeed or to explicitly say it can be called only once.
The documentation says "this function always succeeds" and "call this only to get the first field".

I know I should probably have saved the value of the first call to split_iterator.first() (and reused the value), but the documentation does not say something like "Caller guarantees that this function is called only once".

[Vexu]

It was added with the intention of it only being valid once which the documentation should state more clearly. It could be made to always work by having it call reset but I think that could be more unexpected.

This also applies to all other firsts in the std.mem iterators.