Obfuscated way of accessing a character in string

I found today interesting piece of code:

auto ch = (double(), (float(), int()))["\t\a\r\n\0"]["abcdefghij"];

which works same as:

char str[] = "abcdefghij";
char ch = str['\t'];

Why is it even possible? Especially why is the compiler picking first char from string and using it as subscript instead of throwing error?