C#•8mo ago

❔ Why I can´t use TryParse with a ternary if

It´s a really novice question but I don´t get why this works fine with a normal if:

string[] values = { "12,3", "45", "ABC", "11", "DEF" };

decimal total = 0;
string msg = "";
foreach (string value in values)
{
    decimal parsedValue;

    if (decimal.TryParse(value, out parsedValue))
    {
        total += parsedValue;
    }
    else
    {
        msg += value;
    }
}

Console.WriteLine($"Total: {total}");
Console.WriteLine($"Message: {msg}");

string[] values = { "12,3", "45", "ABC", "11", "DEF" };

decimal total = 0;
string msg = "";
foreach (string value in values)
{
    decimal parsedValue;

    if (decimal.TryParse(value, out parsedValue))
    {
        total += parsedValue;
    }
    else
    {
        msg += value;
    }
}

Console.WriteLine($"Total: {total}");
Console.WriteLine($"Message: {msg}");

But replacing it with

decimal.TryParse(value, out parsedValue) ? total += parsedValue : msg += value;

decimal.TryParse(value, out parsedValue) ? total += parsedValue : msg += value;

Does not work

14 Replies

Angius•8mo ago

A ternary expression returns a value += does not So it cannot be returned from a ternary

David Bernhardt•8mo ago

Oh I get it, thank you!!

cap5lut•8mo ago

just for additional info: theoretically u could do msg += condition ? val1 : val2; but here u would run into the next limitation that the resulting value has to be of same type

JakenVeina•8mo ago

+= does in fact return its value. The issue here is that the two expressions are different types.

Angius•8mo ago

Ah, right

JakenVeina•8mo ago

that one got ke the other day as well, actually

cap5lut•8mo ago

didnt even know about that, but logical since i++ and ++i do too 🤔

arion•8mo ago

total and parsedValue are type decimal while msg and value are type string var cannot infer what you're trying to return but explicitly stating its an object can. eg.

MODiX•8mo ago

arion

REPL Result: Success

string[] values = { "12,3", "45", "ABC", "11", "DEF" };

decimal total = 0;
string msg = "";
foreach (string value in values)
{
    decimal parsedValue;

    // if (decimal.TryParse(value, out parsedValue))
    // {
    //     total += parsedValue;
    // }
    // else
    // {
    //     msg += value;
    // }
    
    object _ = decimal.TryParse(value, out parsedValue) ? total += parsedValue : msg += value;
}

Console.WriteLine($"Total: {total}");
Console.WriteLine($"Message: {msg}");

string[] values = { "12,3", "45", "ABC", "11", "DEF" };

decimal total = 0;
string msg = "";
foreach (string value in values)
{
    decimal parsedValue;

    // if (decimal.TryParse(value, out parsedValue))
    // {
    //     total += parsedValue;
    // }
    // else
    // {
    //     msg += value;
    // }
    
    object _ = decimal.TryParse(value, out parsedValue) ? total += parsedValue : msg += value;
}

Console.WriteLine($"Total: {total}");
Console.WriteLine($"Message: {msg}");

Console Output

Total: 179
Message: ABCDEF

Total: 179
Message: ABCDEF

Compile: 714.770ms | Execution: 64.149ms | React with ❌ to remove this embed.

arion•8mo ago

It leaves for some weird shenanigans you can do, such as

MODiX•8mo ago

arion

REPL Result: Success

var a = 4;
var b = 2;
var x = a += b; 

Console.WriteLine(x);
Console.WriteLine(a);
Console.WriteLine(b);

var a = 4;
var b = 2;
var x = a += b; 

Console.WriteLine(x);
Console.WriteLine(a);
Console.WriteLine(b);

Console Output

6
6
2

6
6
2

Compile: 577.082ms | Execution: 34.267ms | React with ❌ to remove this embed.

arion•8mo ago

Doing a Console.WriteLine (which accepts type object?) will either print a decimal or a string

Console.WriteLine(decimal.TryParse(value, out parsedValue) ? total += parsedValue : msg += value);

Console.WriteLine(decimal.TryParse(value, out parsedValue) ? total += parsedValue : msg += value);

and will document each append operation's new value

David Bernhardt•8mo ago

Great explanation and examples!

Accord•8mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ Why I can´t use TryParse with a ternary if