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c#expression-trees

Caching Compiled Expression tree

How to efficiently cache methods compiled from an expression tree ?

public void SomeToStringCalls()
{
    ToString(i => (i + 1).ToString(), 1);
    ToString(i => (i + 1).ToString(), 2);
    ToString(i => (i + 2).ToString(), 3);
    ToString(i => (i + 2).ToString(), 4);
}

private string ToString<T>(Expression<Func<T, string>> expression, T input)
{
    var method = expression.Compile();
    return method.Invoke(input);
}

Above, every call is going to recompile each expression, even if some are identical. I can't have a Dictionary<Expression<Func<T, string>>, Func<T, string>>() caching the compiled method from the expression because the equals will fails.

Solution

  • I found quite some time ago this article, which is exposing pros & cons of expression caching (with constant extraction... which allows you to compile .Where(t=>t.prop==3) and .Where(t=>t.prop==5) to the same delegate).