The for range Construct

Infinite loop

The condition can be absent like in:

for i:=0; ; i++ or for { }

This is the same as for ;; { } but the ; ; is removed by gofmt. These are infinite loops. The latter could also be written as:

for true { }

But the normal format is:

for { }

If a condition check is missing in a for-header, the condition for looping is and remains always true. Therefore, in the loop-body, something has to happen in order for the loop to be exited after a number of iterations. Always check that the exit-condition will evaluate to true at a certain moment in order to avoid an endless loop! This kind of loop is exited via a break statement, which we’ll study in the next lesson, or a return statement. But, there is a difference. Break only exits from the loop while return exits from the function in which the loop is coded!

Use of for range

The for range is the iterator construct in Go, and you will find it useful in a lot of contexts. It is a very elegant variation used to make a loop over every item in a collection. The general format is:

for ix, val := range coll { }

The range keyword is applied to an indexed collection coll. Each time range is called, it returns an index ix and the copy of value val at that index in the collection coll. So the first time range is called on coll, it returns the first element; that is ix==0 and val==coll[0]==coll[ix]. This statement is similar to a foreach statement in other languages, but we still have the index ix at each iteration in the loop.

Be careful! Here, val is a copy of the value at that index ix in the collection coll, so it can be used only for read-purposes. The real value in the collection cannot be modified through val.

Now, let’s solve the issue we encountered when printing characters of a Unicode string.