I was following the documentation here: http://dlang.org.mirror/spec/arrays.html#slicing and I'm having a problem comparing the returned Slice from a function with an array.

Here's the simplified code:

import std.stdio;
import std.regex;
import std.string;
import std.array;

auto sliceIt(array[string] words_arr) {
  int i = 1;
  string word;
  while(i < words_arr.length) {
    word = words_arr[i];
    if(matchFirst(word, r"^[A-Z]+$")) { break; }
    i++;
  }
  return def_words_arr[1..i];
}

unittest {
  auto words = ["HELLO", "world", "hi", "ENDOFTHERUNWAY"];
  auto resulting_arr = sliceIt(["world", "hi"]);
  assert(resulting_arr == ["world", "hi"]);
}

This produces a compile-time error:

Error: template `std.array.array(Range)(Range r) if (isIterable!Range && !isAutodecodableString!Range && !isInfinite!Range)` is used as a type
Failed: ["~/.local/dlang/dmd-2.108.1/freebsd/bin64/dmd", "-debug", "-unittest", "-main", "-v", "-o-", "words.d", "-Idefinition"]

I was thinking of maybe assigning correct return type for the function, tried it, but got more errors produced by the compiler. Can someone point me to an obvious mistake or lack of understanding?

On Tuesday, 11 June 2024 at 08:29:06 UTC, madwebness wrote:

Correction here, I, of course, meant:

auto resulting_arr = sliceIt(words);

On Tuesday, 11 June 2024 at 08:44:25 UTC, Richard (Rikki) Andrew Cattermole wrote:

While I do understand what you're saying, I'm not sure I understand how to fix the code.

1. Changing function's argument type to Array(string) results in the following error: Error: function declaration without return type.

2. Adding function type Array(string) sliceIt(...) results in the following error: Error: function declaration without return type.

3. Finally, changing function's argument type to string[], so function definition looks like this:

auto extract_arg_names(string[] def_words_arr){...};

results in, what I presume, is a runtime error:

core.exception.AssertError@definition/sliceit.d(42): unittest failure
----------------
??:? _d_unittestp [0x357a31]
??:? void arg.__unittest_L39_C1() [0x302495]
??:? void arg.__modtest() [0x34ba78]
??:? int core.runtime.runModuleUnitTests().__foreachbody6(object.ModuleInfo*) [0x37316a]
??:? int object.ModuleInfo.opApply(scope int delegate(object.ModuleInfo*)).__lambda2(immutable(object.ModuleInfo*)) [0x34dde3]
??:? int rt.minfo.moduleinfos_apply(scope int delegate(immutable(object.ModuleInfo*))).__foreachbody2(ref rt.sections_elf_shared.DSO) [0x380257]
??:? int rt.sections_elf_shared.DSO.opApply(scope int delegate(ref rt.sections_elf_shared.DSO)) [0x382dd1]
??:? int rt.minfo.moduleinfos_apply(scope int delegate(immutable(object.ModuleInfo*))) [0x3801e5]
??:? int object.ModuleInfo.opApply(scope int delegate(object.ModuleInfo*)) [0x34ddb5]
??:? runModuleUnitTests [0x372fa0]
??:? void rt.dmain2._d_run_main2(char[][], ulong, extern (C) int function(char[][])*).runAll() [0x372728]
??:? void rt.dmain2._d_run_main2(char[][], ulong, extern (C) int function(char[][])*).tryExec(scope void delegate()) [0x3726b5]
??:? _d_run_main2 [0x37261e]
??:? _d_run_main [0x3723bf]
??:? main [0x34ba8d]
??:? __libc_start1 [0x82289eaf9]
/usr/src/lib/csu/amd64/crt1_s.S:83 _start [0x30213f]
??:? ??? [0xe83fb403007]
1/1 modules FAILED unittests

PS. Found more correction in the original code. The variable def_words_arr should just be words_arr. Was not paying attention when simplifying the code to post here.

On Tuesday, 11 June 2024 at 09:17:21 UTC, madwebness wrote:

With the following function definition what the function returns is correct and the problem is in the unittest code. Note that writeln() prints what's expected here program fails only when it gets to assert():

auto sliceIt(string[] words_arr) {...};

unittest {
  auto words = ["HELLO", "world", "hi", "ENDOFTHERUNWAY"];
  auto resulting_arr = sliceIt(words);
  writeln(resulting_arr[0]); // => "world"
  assert(resulting_arr[0] == "world"); // => ERROR mentioned in (3) in the previous post.
}

On Tuesday, 11 June 2024 at 09:29:05 UTC, madwebness wrote:

Ran the code exactly as you posted. It works and I found the issue. Apparently, if I add =* to the end of the last element, the assertion fails with the error.

auto words = ["HELLO", "world", "hi", "ENDOFTHERUNWAY=*"];

results in:

core.exception.AssertError@./code.d(23): Assertion failure
----------------
??:? _d_assertp [0x360904]
??:? _Dmain [0x3073c3]

I don't understand why, isn't it supposed to be treated as a string?

On Tuesday, 11 June 2024 at 09:48:36 UTC, madwebness wrote:

auto words = ["HELLO", "world", "hi", "ENDOFTHERUNWAY=*"];

core.exception.AssertError@./code.d(23): Assertion failure
----------------
??:? _d_assertp [0x360904]
??:? _Dmain [0x3073c3]

Ah, my mistake. With the regular expression adjusted to r"^[A-Z]+(=.*)?$" it works just fine. Thank you very much for running the code for me. All very simple, I'm just new to the language.