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    <p>The problem you describe is severe in the sense that evaluating two expressions for <strong>semantic</strong> equality is at least as expensive as compiling the expression. To illustrate this, <a href="http://badecho.com/2012/02/expression-equality-comparer-part-i/" rel="nofollow noreferrer">here</a> is a link to an implementation for expression equality. This implementation is not perfect, for example:</p> <pre><code>MethodA() { MethodB(); } MethodB() { ... } </code></pre> <p>In the example above, <code>MethodA</code> and <code>MethodB</code> are equivalent in the sense that they do the same thing, and you most likely want to consider them as equivalent. For example, building this in C# with compiler optimization enabled will replace the <code>MethodB</code> call with <code>MethodA</code> calls. There are a myriad of issues when comparing code and it is a topic of ongoing research.</p> <p>You should consider a design where expressions are referenced by some kind of key that identifies it if you find out that compiling the expressions is the bottleneck in your application. <strong>By the time you have determined equality you could have already compiled it.</strong></p> <p>To comment on J0HN's answer, it compares the hash code of the body and the parameters, this is by no means a reliable solution, since it does not do a deep evaluation of the expression tree.</p> <p>Also, take a look at <a href="https://stackoverflow.com/questions/283537/most-efficient-way-to-test-equality-of-lambda-expressions">this question</a> as posted in the comments.</p>
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    1. POCaching Compiled Expression tree
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    1. COWouldn't comparing code based on “they do the same thing” require solving the (unsolvable) halting problem?
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    2. CO@svick I think no, because when they are not too obviously equal, we can just treat them as different.
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    3. CO@SargeBorsch But that means dealing with false negatives. To solve it in the "always correct" manor is provably impossible. In fact, proving that two blocks of code always provide the same output for any given input is a famous problem that is provably insolvable.
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