Fails on byte array field

[DamianReeves]

The code fails to work with a byte array field:

    [GenerateImmutable]
    public partial class AccessToken
    {
        readonly string accessKey;
        readonly byte[] secret;
    }

[AArnott]

How does it fail? byte[] isn't immutable, so given immutability is the presumed goal, have you tried ImmutableArray<byte>?

[IanYates]

I had the same problem and then the same forehead slapping realisation that ImmutableList was the answer, although one time I was happy enough with a base64 string since I was using my immutable object as a DTO via JSON.NET and SignalR anyway.
I guess some automatic conversion of common array or collection types to ImmutableList would be handy for newcomers.

[AArnott]

Thanks, @IanYates. Although I'll offer that ImmutableList<T> is a really bad substitute for a byte[] because of ImmutableList<T>'s internal data structure being much more expensive than an array. That's why ImmutableArray<T> is preferable when you don't need fast incremental mutation-by-copy, which is where ImmutableList<T> shines.

We can't automatically convert a byte[] in the source to one of these, because the field you supply ends up in the final code. While we can add a property getter and setter that exposed the field as this other collection type, it would require copying the data on every get and set call, which would be super inefficient.

I suspect the "fix" here is for the IOG generator to flag use of byte[] (or any array type) as an error and suggest use of ImmutableArray<T> instead.

[IanYates]

Good point

We can't automatically convert a byte[] in the source to one of these, because the field you supply ends up in the final code. While we can add a property getter and setter that exposed the field as this other collection type, it would require copying the data on every get and set call, which would be super inefficient.

Although I'm still on the T4 templates where such anarchy can occur :)

Agreed about ImmutableArray making more sense for this purpose.

[AArnott]

Although I'm still on the T4 templates where such anarchy can occur :)

True. :) The T4 approach did let the generator rewrite the fields. That was nice because it could add attributes to the fields (like hiding them from the debugger display by default).

[AArnott]

Given the original repro, the code generation task fails with this error:

The "GenerateCodeFromAttributes" task failed unexpectedly.
System.ArgumentNullException: Value cannot be null.
Parameter name: type
   at Microsoft.CodeAnalysis.CSharp.SyntaxFactory.VariableDeclaration(TypeSyntax type, SeparatedSyntaxList`1 variables)
   at ImmutableObjectGraph.Generation.CodeGen.<>c.<CreateTemplateStruct>b__69_0(MetaField f) in C:\Users\andre\git\ImmutableObjectGraph\src\ImmutableObjectGraph.Generation\CodeGen.cs:line 364
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   at Microsoft.CodeAnalysis.CSharp.SyntaxFactory.List[TNode](IEnumerable`1 nodes)
   at ImmutableObjectGraph.Generation.CodeGen.CreateTemplateStruct() in C:\Users\andre\git\ImmutableObjectGraph\src\ImmutableObjectGraph.Generation\CodeGen.cs:line 361
   at ImmutableObjectGraph.Generation.CodeGen.<GenerateAsync>d__58.MoveNext() in C:\Users\andre\git\ImmutableObjectGraph\src\ImmutableObjectGraph.Generation\CodeGen.cs:line 147
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at ImmutableObjectGraph.Generation.CodeGen.<GenerateAsync>d__56.MoveNext() in C:\Users\andre\git\ImmutableObjectGraph\src\ImmutableObjectGraph.Generation\CodeGen.cs:line 97
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task)
   at CodeGeneration.Roslyn.DocumentTransform.<TransformAsync>d__2.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task)
   at CodeGeneration.Roslyn.Tasks.GenerateCodeFromAttributes.Helper.<<Execute>b__36_0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at CodeGeneration.Roslyn.Tasks.GenerateCodeFromAttributes.Helper.Execute()
   at CodeGeneration.Roslyn.Tasks.GenerateCodeFromAttributes.Helper.Execute()
   at CodeGeneration.Roslyn.Tasks.GenerateCodeFromAttributes.Execute()
   at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute()
   at Microsoft.Build.BackEnd.TaskBuilder.<ExecuteInstantiatedTask>d__26.MoveNext()