如何使用eval从函数返回？

I have a function which is basically like this:

function myfunction(){
    eval("return;");
    echo 'this line has to not show up';
}

For technical reasons, the decision to return (or not) from the function, has to be made in the eval instruction, but the above approach doesn't work. How can I make this work?

You can't. The contents of the eval are considered their own context, so "return" is interpreted as exiting the eval'd string, and returning control to the function. A few alternatives to consider:

• Return a value from the eval string determining the action to take, e.g. if ( eval('return true;') ) { return; }
• Throw an Exception inside the eval'd string, and catch it wherever you call this function.
• Don't use eval in the first place. There is pretty much always a better approach than using eval. Without knowing what you're using this code for, I can't be more specific, but I would strongly recommend changing your design rather than continuing down this route.