arrays.sum([]) or {panic(err)} produces a misleading/obscure error message:

[holder66]

Describe the bug

arrays.sum([]) or {panic(err)} returns "/v/vlib/arrays/arrays.v:253:4: error: operator += not defined on left operand type T"

Reproduction Steps

arrays.sum([]) or {panic(err)}

Expected Behavior

I would like to see an error message about the array being empty

Current Behavior

v/vlib/arrays/arrays.v:253:4: error: operator += not defined on left operand type T

Possible Solution

No response

Additional Information/Context

No response

V version

Current V version: V 0.4.8 df51e84, timestamp: 2024-11-14 13:58:50 +0200

Environment details (OS name and version, etc.)

V full version: V 0.4.8 dad8e3c.df51e84
OS: macos, macOS, 15.0.1, 24A348
Processor: 16 cpus, 64bit, little endian, Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz

getwd: /Users/henryolders
vexe: /Users/henryolders/v/v
vexe mtime: 2024-11-14 15:14:24

vroot: OK, value: /Users/henryolders/v
VMODULES: OK, value: /Users/henryolders/.vmodules
VTMP: OK, value: /tmp/v_507

env VFLAGS: "-use-os-system-to-run"

Git version: git version 2.47.0
Git vroot status: weekly.2024.06-1635-gdf51e840
.git/config present: true

CC version: Apple clang version 16.0.0 (clang-1600.0.26.4)
emcc version: N/A
thirdparty/tcc status: thirdparty-macos-amd64 975f1ad8

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_{Huly®: V_0.6-21302}

[jorgeluismireles]

I think you need to specify the generic type of the argument. Once specified the type of an empty array then you got a panic with more information: Cannot sum up array of nothing. The generic type must overload the addition operator +. Types int, f32 and the like will work. For other types you need to do something like this:

import arrays

struct Str {
	s string
}

fn (m Str) + (n Str) Str {
	return Str{ m.s + n.s }
}

s1 := arrays.sum([Str{'a'},Str{'b'},Str{'c'}])!
println('${s1.s}') // prints: 'abc'

if s2 := arrays.sum([]Str{}) {
	println('${s2.s}') //
} else {
	println('${err}') // prints: Cannot sum up array of nothing
}

See https://play.vlang.io/p/594631bd45

[JalonSolov]

Yes, specifying the type fixes the code, but it doesn't change the fact that the error message is confusing because it doesn't point to your source, it points to a stdlib routine that you can't control.

Error messages should tell you what in your source caused the problem, not where it eventually failed.

[jorgeluismireles]

Maybe the compiler should notify first Cannot sum up array of nothing in the line arrays.sum([]).

Then in the case the user adds elements of type not overriding + like a mere string arrays.sum(['a','b']) notify error: operator += not defined on left operand type string. Actually is not clear that overriding only + is included += too.

[Delta456]

If the length of the array is zero. 0 can also be returned accordingly

[jorgeluismireles]

I think we should have several "different" zeros to return: int, f32, fraction, complex...
arrays.sum works for math.fractions:

import arrays
import math.fractions

zero := fractions.fraction(0,1)
half := fractions.fraction(1,2)
third := fractions.fraction(1,3)

mut fracs := [ zero, half, third ]

if s1 := arrays.sum(fracs) {
	assert s1 == fractions.fraction(5,6)
} else {
	
}

fracs.clear()

if s2 := arrays.sum(fracs) {
	
} else {
	assert err.str() == 'Cannot sum up array of nothing.'
}

// assert 0 == zero <- THIS CANNOT BE DONE

But I'm afraid that above fraction zero is not the same than, to say, integer zero. While fractional zero 0/1 is the same to fractional zero of adding 1/2 and -1/2.

So maybe panicking as is done right now solves the different zeros problem easily.

Or... sum function could return an Option instead of a Result, so for empty you'll have none.