How to get an index in a slice given its subslice?

[proud kettle]

Do you think this is a good (reliable) way to get an end index of the sub slice?

const std = @import("std");

pub fn main() !void {
    const slice = "hello world!";
    const sub = slice[6..8];
    std.log.debug("slice:   {s}", .{slice});
    std.log.debug("sub:     {s}", .{sub});
    std.log.debug("sub end: {d}", .{(@intFromPtr(sub.ptr) + sub.len) - @intFromPtr(slice.ptr)}); // also works without using *.ptr
}

output:

debug: slice:   hello world!
debug: sub:     wo
debug: sub end: 8

[sharp haven]

Well sub's end index is 1, not 8

11 is the end index of slice

Or I don't understand what you're trying to do

[zenith cipher]

I dont know of any other way to do it, no

[proud kettle]

sorry, how sub's end index could be 1?

       0123456789
slice: hello world!
sub  :       wo
             ^ (start:6)
               ^ (end:8)

[sharp haven]

You mean in relation to slice, I was not sure tha'ts what you meant

[proud kettle]

"No" in which sense? Like, you don't know the other way or the way I suggested is the bad one?

[proud kettle]

yeah, I meant the end idx relative to the entire slice

[sharp haven]

By end you mean the last index that's part of the slice, or one position after?

So maybe like this? subtract one then add one?
std.debug.print("sub end: {d}", .{@intFromPtr(&sub[sub.len - 1]) - @intFromPtr(&slice[0]) + 1});

[zenith cipher]

I dont think theres any other way to do it
I dont think it's necessarily good practice since its hard to read but if its the only way its fine

[sharp haven]

It's a bit more verbose though at least in my mind captures the intention better.

[safe socket]

we do have pointer subtraction now, so it's just sub.ptr + sub.len - slice.ptr

[proud kettle]

main.zig:8:62: error: expected type 'usize', found '[*:0]const u8'
    std.log.debug("sub end: {d}", .{sub.ptr + sub.len - slice.ptr});
                                                        ~~~~~^~~~

[safe socket]

probably not released yet

[proud kettle]

:)

[safe socket]

yeah not in 0.13.0

[proud kettle]

to be honest I don't think this is a good one. If you pass a sub that is len=0, you'll get a panic with an integer overflow. However, I agree this one is more instructive "conceptually" but more cryptic in practice because the amount of ops shoved in it.