C#•16mo ago

❔ Casting range to bytes?

byte[] bytes = Enumerable.Range(0, 256).Cast<byte>().ToArray();

byte[] bytes = Enumerable.Range(0, 256).Cast<byte>().ToArray();

The result: System.InvalidCastException : Unable to cast object of type 'System.Int32' to type 'System.Byte'. Why? This should work! Why doesn't this work!?

8 Replies

BenMcLean•16mo ago

I know that this is a valid cast, because this should be equivalent to that:

byte[] bytes = Enumerable.Range(0, 256).Select(i => (byte)i).ToArray();

byte[] bytes = Enumerable.Range(0, 256).Select(i => (byte)i).ToArray();

and yet using Select works just fine.

DaVinki•16mo ago

It's so sad that this isn't a thing But it doesn't work because it doesn't do explicit casting like you do in your Select It uses the is keyword, guaranteeing no loss of data If it's not to an inherited type, it won't work For this instance, int is not byte But given any reference type, say Rectangle, that is object

BenMcLean•16mo ago

Oh, that makes sense. The Cast method only works if the type being cast from is the type being cast to Thanks

DaVinki•16mo ago

Or if you had a stream of boxed objects of type object, if you know 100% they are all Rectangle, you can do .Cast<Rectangle>() But yeah it's a shame there is no casting method that allows casting numbers that isn't select

MODiX•16mo ago

daVinki#5278

REPL Result: Success

const int Lengths = 5;

Console.WriteLine("rectangle -> object cast");
Enumerable.Range(1, Lengths)
    .Select(a => new Rectangle(a, a))
    .Cast<object>()
    .ToList()
    .ForEach(Console.WriteLine);

Console.WriteLine("\nobject -> rectangle cast");
Enumerable.Range(1, Lengths)
    .Select(a => (object)new Rectangle(a, a))
    .Cast<Rectangle>()
    .ToList()
    .ForEach(Console.WriteLine);

record Rectangle(int L, int W);

const int Lengths = 5;

Console.WriteLine("rectangle -> object cast");
Enumerable.Range(1, Lengths)
    .Select(a => new Rectangle(a, a))
    .Cast<object>()
    .ToList()
    .ForEach(Console.WriteLine);

Console.WriteLine("\nobject -> rectangle cast");
Enumerable.Range(1, Lengths)
    .Select(a => (object)new Rectangle(a, a))
    .Cast<Rectangle>()
    .ToList()
    .ForEach(Console.WriteLine);

record Rectangle(int L, int W);

Console Output

rectangle -> object cast
Rectangle { L = 1, W = 1 }
Rectangle { L = 2, W = 2 }
Rectangle { L = 3, W = 3 }
Rectangle { L = 4, W = 4 }
Rectangle { L = 5, W = 5 }

object -> rectangle cast
Rectangle { L = 1, W = 1 }
Rectangle { L = 2, W = 2 }
Rectangle { L = 3, W = 3 }
Rectangle { L = 4, W = 4 }
Rectangle { L = 5, W = 5 }

rectangle -> object cast
Rectangle { L = 1, W = 1 }
Rectangle { L = 2, W = 2 }
Rectangle { L = 3, W = 3 }
Rectangle { L = 4, W = 4 }
Rectangle { L = 5, W = 5 }

object -> rectangle cast
Rectangle { L = 1, W = 1 }
Rectangle { L = 2, W = 2 }
Rectangle { L = 3, W = 3 }
Rectangle { L = 4, W = 4 }
Rectangle { L = 5, W = 5 }

Compile: 855.536ms | Execution: 168.607ms | React with ❌ to remove this embed.

Aaron•16mo ago

because it effectively does

foreach (object o in enumerable)
    yield return (T)o;

foreach (object o in enumerable)
    yield return (T)o;

that cast there is an unboxing conversion, which can't do this

MODiX•16mo ago

Windows10CE#8553

REPL Result: Failure

object o = (int)27;
byte b = (byte)o;

object o = (int)27;
byte b = (byte)o;

Exception: InvalidCastException

- Unable to cast object of type 'System.Int32' to type 'System.Byte'.

- Unable to cast object of type 'System.Int32' to type 'System.Byte'.

Compile: 477.088ms | Execution: 29.689ms | React with ❌ to remove this embed.

Accord•16mo 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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❔ Casting range to bytes?