There are much better explanations by people who really know about functional programming so the next few posts on F# are more an exercise for my brain than anything else. But maybe you will find them useful...
So I haven't heard of the tuple since watching boring educational videos on database theory 10 years ago. But alas the tuple appears again as I'm learning F# and also digging into some mathematical concepts again. It's actually been there all along as I declared a singleton or joined database tables. A tuple is basically a finite sequence of objects that are in a particular order and can contain the same object more than once. It is also immutable (Aka, cant be modified). An example of a tuple could be a first name, last name and age. In C# we may define it as a generic triple (a tuple with three items) class as follows:
public class Triple<A,B,C>
{
private A value1;
private B value2;
private C value3;
public Person(
A value1,
B value2,
C value3)
{
this.value1 = value1;
this.value2 = value2;
this.value3 = value3;
}
public A Value1 { get { return this.value1; } }
public B Value2 { get { return this.value2; } }
public C Value3 { get { return this.value3; } }
}
Then define our person as this triple:
Triple<string, string, int> person =
new Triple<string, string, int>("Richard", "Nixon", 61);
We could then set other values to the contents of the triple if we wanted:
string firstName = person.ValueA;
string lastName = person.ValueB;
int age = person.ValueC;
Easy enough right? Well lets see how we could do the same thing in F#. First off we don't have to create or instantiate a tuple class (This is actually done under the covers as we will see in a moment). We simply set the variable equal to a comma separated list of objects as follows:
let person = "Richard", "Nixon", 61
And voila! We have a tuple (A triple to be precise)... Now to set the contents of the tuple to other variables we simply do the following:
let firstName, lastName, age = person
Here we just set the individual firstName, lastName and age variables to the corresponding values in the tuple. On the other hand if we just want the first name we can block out the last name and age with the underscore placeholder ("_") and just get the first name:
let firstName, _, _ = person
or we can just get the last name and the age by blocking out the first name. You get the point...
let _, lastName, age = person
F# uses "pattern matching" to match up the variables listed, with the values in the tuple. Now as mentioned before, under the covers F# does actually use generic tuple types as seen when working with a tuple from F#...
in C#...
In reflector we can see that there are tuple definitions for up to 7 items:
Edgar Sanchez has a nice blog entry on tuples here.