Why can I write a for loop that doesn't modify the counter?-CodePudding

This code seems to be valid Dart code, even though the last part of the for loop declaration i missing:

for( int i=0; i<1; ){ // Missing i  
  // Do something
}

The result is an infinite loop.

Why is this not considered a syntax error? There's no mention of this "feature" in the Dart Language Tour.

CodePudding user response：

Well it is a feature, it just gives you an extra control over your for loop. You are technically still following the contract of for-loop but stating that, incremental part will be handled by you later on.

This t just gives you a chance to do the increment within the for loop instead of doing it on the fly.

  for (int i = 0; i < 10; ) {
    i = 'test'.length   i;
    print('test $i');
  }

CodePudding user response：

The same holds for C, C , java: even for (;;) { is possible.

Consider other ways of using an index (java):

for (int i = 0; i < s.length(); ) {
    ...
    int i2 = s.indexOf(',', i   1);
    if (i2 == -1)
        i2 = s.length();
    String w = s.substring(i, i2);
    ...
    i = i2;
}

In general one can only in specific cases guarantee that a program terminates. So the value of such requirement would be relative.