Abstract supertype of ranged streams mapping a range of discrete indices to elements of the stream, and supporting operations that produce a subrange of indexed elements. The type parameter Subrange abstracts the type of the resulting subrange. A subrange may be obtained from an instance of Ranged using the span and measure operators.

Often, in a List or sorted map for example, an index and its element are distinct values. Sometimes, in a sorted set for example, the index and element are identical.

The span operator accepts the first and last indices of the subrange.

print("hello world"[0..4]); //prints "hello"
print("hello world"[6..6]); //prints "w"

If the last index is smaller than the first index, the subrange is reversed.

print("hello world"[4..0]); //prints "olleh"

If the range of indices identified by the first and last indices is outside the range of indices of this object, an empty subrange is produced.

print("hello world"[-5..-1]); //prints ""
print("hello world"[11..11]); //prints ""

The first index may be omitted, implying that the subrange extends forward from the smallest possible index (in this case runtime.minIntegerValue) to the given index.

print("hello world"[...4]) //prints "hello"

If the first index is before the first index of this object, the first index of the object is used.

print("hello world"[-5...]); //prints "hello world"

The last index may be omitted, implying that the subrange extends forward from the given index to the largest possible index (in this case runtime.maxIntegerValue).

print("hello world"[6...]) //prints "world"

If the last index is after the last index of this object, an empty subrange is produced. (A reversed subrange is never produced.)

print("hello world"[11...]); //prints ""

The measure operator accepts the first index and maximum length of the subrange.

print("hello world"[6:5]) //prints "world"
print("hello world"[6:0]) //prints ""

If the length is nonpositive, the subrange is empty. If the range of indices identified by the first index and length is outside the range of indices of this object, an empty subrange is produced. (A reversed subrange is never produced.)

print("hello world"[-3:3]) //prints ""
print("hello world"[11:3]) //prints ""
print("hello world"[6:-3]) //prints ""

The span and measure operations must be consistent. That is, for every pair of indices x and y in the ranged object ranged such that y does not occur before x and the span ranged[x..y] has length n:

• ranged[x..y]==ranged[x:n].