csharp.md

csharp

• interpolated string
• try catches and finally
• Struct reference
  • readonly ref argument
  • readonly ref field
• Number conversion
  • convert int to hex
• Templates
  • implicit type inference
• Troubleshoot
  • The expression being assigned to 'SomeConstVarName' must be constant csharp(CS0133)
• macro
  • disable warning

interpolated string

code	result	notes
${12:D5}	00012	left pad with zero
${12.109:F2}	12.11	decimal places w/rounding
[${12,5}]	[ 12]	width with space padding
[${12,-5}]	[12 ]	width with space padding (left align)
${DateTimeOffset.UtcNow:yyyyMMddTHHmmssZ}	20250417T211031Z	year month day hour minutes seconds gmt
${DateTimeOffset.Now:yyyyMMddTHHmmsszz}	20250417T231031+02	year month day hour minutes seconds zone (hours offset)

try catches and finally

try
{
    // NOTE: the finally will executed after return
    return;
}

finally
{
    System.Console.WriteLine("FINALLY");    
}

System.Console.WriteLine("NEVER REACHED CODE");

Struct reference

readonly ref argument

Vector3 v = Vector3.One;

float Sample(Vector3 v)
{
    return v.X;
}
System.Console.WriteLine(Sample(v));

float ReadonlySample(in Vector3 v) // ensure that struct argument is readonly, passed by ref
{
    // v.X = 2; // <-- this generate follow compiler error
    // error CS8332: Cannot assign to a member of variable 'v'
    // or use it as the right hand side of a ref assignment
    // because it is a readonly variable

    return v.X;
}
System.Console.WriteLine(ReadonlySample(v));

compiles to:

// Vector3 v2 = Vector3.One;
IL_0001: call valuetype [System.Numerics.Vectors]System.Numerics.Vector3 [System.Numerics.Vectors]System.Numerics.Vector3::get_One()
IL_0006: stloc.0
// Console.WriteLine(Sample(v2));
IL_0007: nop
IL_0008: ldloc.0
IL_0009: call float32 test_console.Sample::'<Main>g__Sample|0_0'(valuetype [System.Numerics.Vectors]System.Numerics.Vector3)
IL_000e: call void [System.Console]System.Console::WriteLine(float32)
// (no C# code)
IL_0013: nop
// Console.WriteLine(ReadonlySample(in v2));
IL_0014: nop
IL_0015: ldloca.s 0
IL_0017: call float32 test_console.Sample::'<Main>g__ReadonlySample|0_1'(valuetype [System.Numerics.Vectors]System.Numerics.Vector3&)
IL_001c: call void [System.Console]System.Console::WriteLine(float32)

readonly ref field

using System.Numerics;

public ref struct ReadonlyTest
{

    public ref readonly Vector3 v;

    public ReadonlyTest(ref Vector3 _v)
    {
        v = ref _v;
    }
}

public class Sample
{

    static void Main(string[] args)
    {
        var v = new Vector3(1, 2, 3);

        var test = new ReadonlyTest(ref v);

        v.X = 10;

        var x = v.X;

        var x2 = test.v.X;

        System.Console.WriteLine($"{x} {x2}"); // expects 10 10
    }

}

compiles to:

// float x = _v.X;
IL_002b: ldloc.0
IL_002c: ldfld float32 [System.Numerics.Vectors]System.Numerics.Vector3::X
IL_0031: stloc.2
// float x2 = readonlyTest.v.X;
IL_0032: ldloca.s 1
IL_0034: ldfld valuetype [System.Numerics.Vectors]System.Numerics.Vector3& ReadonlyTest::v
IL_0039: ldfld float32 [System.Numerics.Vectors]System.Numerics.Vector3::X
IL_003e: stloc.3

Number conversion

convert int to hex

int a = 10;
var hexStr1Digit = a.ToString("X"); // "A"
var hexStr2Digit = a.ToString("X2"); // "0A"

Templates

implicit type inference

• ref

Troubleshoot

The expression being assigned to 'SomeConstVarName' must be constant csharp(CS0133)

The expression being assigned to 'Vector3D.Zero' must be constant [netcore-sci]csharp(CS0133)

public const SomeType SomeConstVarName = new SomeType(10);

can solve the problem by declaring the assigned value as a public static readonly field like the following

public static readonly SomeType SomeConstVarName = new SomeType(10);

macro

disable warning

to disable specific warning CSXXXX

#pragma warning disable CSXXXX
...
#pragma warning restore CSXXXX