Question

I’d like to know if it is possible to use an expression as a variable/parameter in C#. I would like to do something like this:

int x = 0; public void g() {    bool greaterThan = f('x>2');    bool lessThan = f('x<2'); } public bool f(Expression expression) {    if(expression)        return true;    else        return false; } 

Here’s what I don’t want to do:

int x = 0; public void g() {     bool greaterThan = f(x, '<', 2); }  public bool f(int x, char c, int y) {     if(c == '<')        return x < y;     if(c == '>')        return x > y; } 

Really what I’m getting at is a way to get around using a switch or series of if statements for each of: < > <= >= == !=. Is there a way to do it?

Edit: Suppose that the expression is a string, like ‘x < 2’. Is there a way to go from the string to a predicate without using a series of if statements on the condition?

Answer 1

Its very possible, just not in the exact syntax you have.

int x = 0; public void g() {    bool greaterThan = f(i => i > 2, x);    bool lessThan = f(i => i < 2, x); } public bool f(Func<int,bool> expression, int value) {    return expression(value); } 

Actually, this should be closer to what you want.

int x = 0; public void g() {    bool greaterThan = f(() => x > 2);    bool lessThan = f(() => x < 2); } public bool f(Func<bool> expression) {    return expression(); } 

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Reply to Edit

If you want be able to say f("x < 2"), it’s going to be almost impossible. Ignoring parsing it (which could get nasty), you have to capture the value of x, but its just a character to f, which makes it pretty much impossible.