nullpropagationvisitor's Introduction

NullPropagationVisitor

Expression tree is an amazing feature of C#, however it only supports a limited subset of C# features.
While there is no native support to null propagation operator a?.b, this library can do the job as an expression visitor.
Just call Visit method of the visitor and you are done!

As well the ?. operator, the visitor evaluates its left-hand operand no more than once.
You can use projects like ReadableExpressions to check the expression returned by visitor.

Examples of use

Check some examples of use in unit tests

Transformation

It works from the basic cenarios:

Expression<Func<string, int>> ex = str => str.Length;

which become something like

(string str) =>
{
    string caller = str;

    return (caller == null) ? null : (int?)caller.Length;
}

To the complex ones

Expression<Func<string, char>> ex = str => str == "foo" ? 'X' : Self(str).Length.ToString()[0];

which become something like

(string str) => (str == "foo")
    ? (char?)'X'
    : {
        string caller =
        {
            int? caller =
            {
                string caller = Program.Self(str);

                return (caller == null) ? null : (int?)caller.Length;
            };

            return (caller == null) ? null : ((int)caller).ToString();
        };

        return (caller == null) ? null : (char?)caller[0];
    }

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nullpropagationvisitor's Issues

The Visitor changes expression type

Hi,

following test will not pass:

#nullable enable

record Foo(string? Name);

Expression<Func<Foo, object?>> propertyLambda = foo => foo.Name;

var visitor = new NullPropagationVisitor(true);
var result = visitor.Visit(propertyLambda); // returns Expression<Func<Foo, string?>>

Assert.IsInstanceOfType(result, typeof(Expression<Func<Foo, object?>>));

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