Get Attribute object from INamedTypeSymbol.GetAttributes() i.e. AttributeData object?

Question

I have defined the following attribute

[AttributeUsage(AttributeTargets.Class)]
class DemoAttribute : Attribute
{
  public string SomeInfo { get; }

  public DemoAttribute(string someInfo)
  {
    this.SomeInfo = someInfo;
  }
}

which can be applied to some class as follows:

[Demo("hello world")]
class Program { }

An INamedTypeSymbol variable namedTypeSymbol pointing to the Program class is provided to me with which I managed to get the name of the attribute.

foreach(var attr in namedTypeSymbol.GetAttributes())
{
  if(attr.AttributeClass.Name == "DemoAttribute") { ... }
}

But how do I access what was set as SomeInfo ?

Answer 1

There are two ways you can pass arguments to attributes. Either by setting the property ( [Demo(SomeInfo="hello world")] ) or via the constructor, as you are doing. If you used the named approach, Ponas would be correct that the solution lies in NamedArguments .

However, as you are using the constructor, the data is located in ConstructorArguments . This is an array of TypedConstant , from which you can get the value "hello world" :

string attributeData = (string)attr.ConstructorArguments[0].Value;