ExpressionEvaluator

Evaluates LINQ Expressions and provides the result

This library allows you to do the following:

Expression<Func<Model, string>> expression = m => m.Property;
string propertyValue = expression.Evaluate(Model);
Debug.Assert(propertyValue == Model.Property);

Why?

Evaluating linq expressions can be done by calling the Compile method, but the compilation process is slow. Therefore one needs to do some sort of caching to avoid compiling the expressions on every call. This is annoying and error prone. Much better to quickly evaluate the expression with a small penalty:

Processor=Intel Core i7-4500U CPU 1.80GHz (Haswell), ProcessorCount=4
Frequency=2338335 Hz, Resolution=427.6547 ns, Timer=TSC
dotnet cli version=1.0.3
  [Host]     : .NET Core 4.6.25009.03, 64bit RyuJIT
  DefaultJob : .NET Core 4.6.25009.03, 64bit RyuJIT

Computing an expensive math operation (Math.Pow(5.2))

Method	Mean	Error	StdDev	Median
CompileEveryTime	88,627.70 ns	7,257.2503 ns	21,284.2588 ns	76,880.76 ns
CompileOnce	50.01 ns	0.4483 ns	0.4193 ns	50.16 ns
Evaluate	1,919.45 ns	34.4638 ns	28.7788 ns	1,916.77 ns

Accessing a property;

Method	Mean	Error	StdDev
CompileEveryTime	78,608.9694 ns	1,552.6065 ns	2,370.9942 ns
CompileOnce	0.8400 ns	0.0444 ns	0.0415 ns
Evaluate	915.2006 ns	13.9449 ns	13.0441 ns

So Evaluate is 1-2 order of magnitudes faster than compiling every time, although much much slower than caching the compiled function. If you can predict that the expressions you will use will be few, compiling and caching is still a better option. Otherwise, evaluate away!