C# Expression tree, using expression with static type of expression for lambda invocation

Question

I am stuck trying to make the dictionary values generic in the following code. I would like to use Expression as a dictionary key and not Expression<Action>. If I change the code to use Expression I get an error. It would be great if the solution would involve Expression.Convert so I would not be trying to make an Expression generic by adding Action as a generic parameter.

Expression<Action> test = () => Console.WriteLine("Hello world");

var dict = new Dictionary<string, Expression<Action>> {["foo"] = test};

var functionDef = Expression.Property(Expression.Constant(dict), "Item", Expression.Constant("foo"));

var intermediate = Expression.Lambda(functionDef);

Expression.Invoke(Expression.Invoke(Expression.Constant(intermediate)));

Error if I use generic Expression instead of Expression<Action> as a dictionary type:

Unhandled exception. System.ArgumentException: Expression of type ‘System.Linq.Expressions.Expression’ cannot be invoked (Parameter ‘expression’)

c++expression trees

tymtam · Answer

I'm not sure what you're issue here is, but maybe you don't need expressions.

Here is an expression-less example:

var d = new Dictionary<string, Action<string>>() 
{
    { "hello", name => Console.WriteLine($"Hello {name}") },
    { "bye", name => Console.WriteLine($"Bye {name}!. Have a great day!") }
};

d["hello"]("Node.JS");
d["bye"]("Node.JS");

This prints:

Hello Node.JS
Bye Node.JS!. Have a great day!

C# Expression tree, using expression with static type of expression for lambda invocation

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