IEnumerable Select

Question

Can someone explain why the following line of C# doesn't behave the same as the following foeach block?

string [] strs = {"asdf", "asd2", "asdf2"};
strs.Select(str => doSomething(str));


foreach(string str in strs){
  doSomething(str);
}

I put a breakpoint inside of doSomething() and it doesn't fire in the Select but it does with the foreach.

TIA

Answer 1

This is because LINQ queries are deferred. The lambda passed to the Select method is actually executed when you access the result.

Try:

string [] strs = {"asdf", "asd2", "asdf2"};
var result = strs.Select(str => doSomething(str));

foreach(var item in result) {
}

Answer 2

The Linq query won't be processed until you convert it to an Enumarable using ToList(), ToArray(), etc.

And by the way the equivalent to your foreach statement is something like this:

strs.ForEach(doSomething);

strs.ToList().ForEach(doSomething);

or

Array.ForEach(strs, doSomething);