Description:
------------
Invalid offset access triggers some kind of errors for strings (and of course arrays):

$str = 'abc';

echo $str[TRUE]; // Notice: String offset cast occurred
echo $str[NULL]; // Notice: String offset cast occurred
echo $str[[]]; // Warning: Illegal offset type

But it triggers no error when variable is integer, float or bool, which is inconsistent:

$int = 123;

echo $int[1]; // no error
echo $int[TRUE]; // no error
echo $int[[]]; // no error

Test script:
---------------
https://3v4l.org/JCXR1

<?php

$str = 'abc';

echo $str[TRUE]; // Notice: String offset cast occurred
echo $str[NULL]; // Notice: String offset cast occurred
echo $str[[]]; // Warning: Illegal offset type

$int = 123;

echo $int[1]; // no error
echo $int[TRUE]; // no error
echo $int[[]]; // no error

$bool = TRUE;

echo $bool[1]; // no error
echo $bool[TRUE]; // no error
echo $bool[[]]; // no error


Expected result:
----------------
trigger errors