concatenate 3 **comptime-unknown** strings but can't afford to use try catch or if

[dusty rivet]

reason I can't use this is because I am sending data to a C function which can't use errors

[shadow basin]

?
catch the errors in your own code before sending it to the C function

you cant concatenate without the possibility of errors because allocation can always fail

[dusty rivet]

hmm, let me give my code example

pub fn send(x: header_with_body) []const u8 {
    const allocator = std.heap.page_allocator;
    const dz = [_][]const u8{ x.header, "\n\n", x.body };
    const res = try std.mem.concat(allocator, u8, &dz);
    return res;
}

error: Function expected to return []const u8, but is returning whatever![]const u8

how can I make this function use std.mem.concat(allocator, u8, &dz); but not return an error

[shadow basin]

youd just do const res = std.mem.concat(allocator, u8, &dz) catch return "server_error"

but there's something wrong with that too

now the function can either return a heap allocated string or a statically allocated string
which is bad
since you have to free heap allocated strings but cant free statically failed allocated strings

I dont understand what issue youre trying to solve either
this function can return an error, there's no reason it shouldnt be able to
you only cant return an error from a function that follows the C calling convention

[dusty rivet]

ya, this function is used in some other function which returns something to C. and I get error callConv(.C) type returning functoin can't return errors

[shadow basin]

yeah so the issue isnt with this function
the issue is in that function which is marked callconv(.C) and is calling this function

show me that function

[dusty rivet]

uh, its very complex, like then that function is inside a wrapper which is called by another function, then passed as argument to other function.... its huge code!
Now, if I go and add ! to this it will take me through all my source code reaching the c file.

so I was trying if it was possible we can make this function not return an error and catch it in some way

[shadow basin]

well either way
just simply dont return an error from the callconv(.C) function lol
catch it in the body and do something else

[dusty rivet]

yes, let me try and I'll get back

[dusty rivet]

that error does seems vanished, but maybe taken over by another error:
can you just quickly please tell me the code to do this correctly:

pub fn path(of: []const u8, is: []const u8) bool {
    const res = std.mem.tokenizeAny(u8, of, " ");
    if (std.mem.eql(u8, res.index(3), is)) {
        return true;
    }
    return false;
}

like, I want to get the 3rd index in zig, similar code in python:

of.split(" ")[3]

[shadow basin]

TokenIterator doesnt have a .index() method
and res needs to be mutable

[dusty rivet]

hmm, can you please tell me a way to split string with delimiter " " like the code and get the 3rd index of it.

[shadow basin]

youd do something like

_ = res.next().?;
_ = res.next().?;
third_index = res.next().?;

note that this asserts that there are at least three items in the iterator

[dusty rivet]

🥹 we are back with !

[shadow basin]

and the reason you cant just take an index is because it's lazy
it's not a list
you cant get the third item without computing the second item and you cant get the second item without computing the first one

[dusty rivet]

the function containing it won't give an an error right?

[shadow basin]

no
.next() reutrns a ?[]const u8

but again
if there arent at least three entries in that iterator, this will crash your program on Debug/ReleaseSafe builds and cause illegal behavior on ReleaseFast builds

so if you arent 100% sure that's the case, you should handle those cases

[dusty rivet]

error: expected type '*mem.TokenIterator(u8,.any)', found '*const mem.TokenIterator(u8,.any)'

I am getting this for some reason

[shadow basin]

yeah
because you declared res as a constant

even though it needs to be mutated to get the next token

[dusty rivet]

OH WOW!

I can't believe it, it is working

Thanks alot!!!!

[shadow basin]

no problem