Daniel Palme

Daniel Palme

.NET consultant from Germany.

Blog > Reflection vs. compiled expressions vs. delegates - Performance comparision

Reflection vs. compiled expressions vs. delegates - Performance comparision

I'm currently working on an application which uses reflection to create a generic UI. Therefore I was interested in the performance impact of reflection. In this post I will do a comparison between the various possibilities to access a property.

The test setup

The following methods are used to access a property called Name in a class Person:

Access the property directly:

string name = p.Name;

Use reflection:

var property = p.GetType().GetProperty("Name");
string name = (string)property.GetValue(p, null);

This test is executed twice. First the PropertyInfo is created in every iteration. In the second test one instance is reused.

Use compiled expression:

ParameterExpression arg = Expression.Parameter(p.GetType(), "x");
Expression expr = Expression.Property(arg, "Name");

var propertyResolver = Expression.Lambda<Func<Person, object>>(expr, arg).Compile();

string name = (string)propertyResolver(p);

This test is also executed twice. First the Expression is created in every iteration. In the second test one instance is reused.

Use delegates:

ParameterExpression arg = Expression.Parameter(p.GetType(), "x");
Expression expr = Expression.Property(arg, "Name");

var propertyResolver = Expression.Lambda(expr, arg).Compile();

string name = (string)propertyResolver(p);

This seems to be the same as the test with the compiled expression. But there is a subtle change: The lambda is created without type information.

Each test is executed 1.000.000 times and the overall time is measured.

The results


TestDuration [ms]
Regualar property31
Reflection with cached PropertyInfo510
Compiled Expression286.879
Cached compiled Expression58
Cached delegate3008


Using the property is of course the fasted way to get the value of a (known) property. But also reflection is not that slow, especially when you reuse the PropertyInfo object.
Compiling an expression is a time consuming operation, but if you reuse the compiled expression the performance is equal to the regular property access. Compilation of expressions only makes sense, if you have to process a lot of objects.
Delegates are relatively slow, because type information is missing compared to compiled expressions.



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Tags: .NET, C#

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Miguel Angelo

Miguel Angelo


The cached delegate time of 3008ms makes no sense... it should be faster than the no-cache version of itself, that took 299.173ms... shouldn't it?



It is faster. I think you are misinterpreting the numbers. The '.' is not used as a decimal separator but as a grouping symbol.
Sebastiaan Dammann

Sebastiaan Dammann

06/07/2013 | http://damsteen.nl/

For some reason the tests yields different results here. The "Cached delegate" is actually quite a bit faster than "Cached compiled Expression". The cached delegate takes around 50 ms.



Thanks for this!

If anyone is interested, here's the code for the compiled setter (my apologies if the formatting gets messed up):

ParameterExpression arg = Expression.Parameter(typeof (Person));
Expression expr = Expression.Property(arg, propertyName);
Expression<Func<Person, string>> get = Expression.Lambda<Func<Person, string>>(expr, arg);
Getter = get.Compile();

var member = get.Body;
var param = Expression.Parameter(typeof (string), "value");
Setter =
Expression.Lambda<Action<Person, string>>(Expression.Assign(member, param), get.Parameters[0], param)


02/12/2014 | http://dev.unclassified.de/

Thank you very much for this brilliant piece of code, both the getter and the setter for compiled expressions. I've been able to build a simple custom O/RM with model attributes around this in a day (~1000 loc) and by measurements with reading 45000 records it takes around 1.5 the time of assigning directly from DbDataReader to model properties. With much less code to write and to maintain!



thanks for this code, helped me alot.

What about this line? I use it for my O/R, where I need fast execution, but yet a generic (object) accessor in the base class. It took about 60ms on my machine:

// Dictionary for the base class. No type information needed!
var d = new Dictionary<string, Func<object, object>>(StringComparer.OrdinalIgnoreCase);

// Filling the dictionary in the derived class
d.Add("Name", (per) => { return ((Person)per).Name; });

// Measuring (60ms!)
for (int i = 0; i < 1000000; i++)



The Setter for completeness:

// Base Schema Class (no types)
var setProperty = new Dictionary<string, Action<object, object>>(StringComparer.OrdinalIgnoreCase);

// Derived Class
setProperty.Add("Name", (n, v) => ((Person)n).Name = (string)v);

// Call
setProperty["Name"](p, Value);