Detects for loops that use length member of some storage array in their loop condition and don't modify it SLITHER-W1088
Performance
Major
Detects for loops that use length member of some storage array in their loop condition and don't modify it.
Exploit Scenario
contract C
{
uint[] array;
function f() public
{
for (uint i = 0; i < array.length; i++)
{
// code that does not modify length of `array`
}
}
}
Since the for loop in f doesn't modify array.length, it is more gas efficient to cache it in some local variable and use that variable instead, like in the following example:
contract C
{
uint[] array;
function f() public
{
uint array_length = array.length;
for (uint i = 0; i < array_length; i++)
{
// code that does not modify length of `array`
}
}
}
Recommendation
Cache the lengths of storage arrays if they are used and not modified in for loops.
Learn more
cache-array-length on Slither's wiki.