What are intervals?

An interval is a sequence of values of the same type between a given pair of endpoint values. Gosu provides native support for intervals. For instance, the set of integers beginning with 0 and ending with 10 is an integer interval. This interval contains the values 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. The Gosu syntax for this set of integers is 0..10. Intervals are particularly useful for concise, readable for loops.

For example, consider this concise, readable code:

for (i in 0..10) {
  print("The value of i is " + i)
}

This code prints the following:

The value of i is 0
The value of i is 1
The value of i is 2
The value of i is 3
The value of i is 4
The value of i is 5
The value of i is 6
The value of i is 7
The value of i is 8
The value of i is 9
The value of i is 10

This code replaces the more verbose and harder-to-read design pattern:

var i = 0
while( i <= 10 ) {
  print("The value of i is " + i)
  i++
}

Intervals do not need to be numbers. Intervals can be of many types including numbers, dates, dimensions, and names. Gosu includes built-in shorthand syntax with a double period (..) for intervals for dates and common number types, such as the previous 0..10 example. The built-in shortcut works with the types Integer, Long, BigInteger, BigDecimal, and Date. All decimal types map to the BigDecimal interval.

You can also add custom interval types that support any type that supports iterable comparable sequences. You can then use your new intervals in for loop declarations.

If you need to get a reference to the interval’s iterator object (java.lang.Iterator), call the iterate method, which returns the iterator.

Omitting an initial or ending value

In the simplest case, a Gosu interval iterates from the beginning endpoint value to the ending endpoint value, including the values at both ends. For example, 0..5 represents the values 0, 1, 2, 3, 4, 5.

In some cases, you want to exclude the beginning value but you still want your code to show the beginning value for code legibility. In other cases, you want to exclude the endpoint value from the interval.

If omitting the initial or ending value results in an empty set of values, iterating over the interval does not occur.

To exclude an endpoint in Gosu, type the pipe "|" character:

To omit the value of the starting endpoint, type the pipe character after the starting endpoint.
To omit the value of the ending endpoint, type the pipe character before the ending endpoint.
To do make both endpoints open, type the pipe character before and after the double period symbol.

Compare the following examples:

0..5 represents the values 0, 1, 2, 3, 4, 5.
0|..5 represents the values 1, 2, 3, 4, 5.
0..|5 represents the values 0, 1, 2, 3, 4.
0|..|5 represents the values 1, 2, 3, 4.
0..|0 does not iterate.
0|..|1 does not iterate.