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// $substr returns an empty string if the position argument is out of bounds. SERVER-6186
t = db.jstests_aggregation_server6186;
t.drop();
t.save({});
function substr(string, pos, n) {
return t.aggregate({$project: {a: {$substr: [string, pos, n]}}}).toArray()[0].a;
}
function expectedSubstr(string, pos, n) {
if (n < 0) {
// A negative value is interpreted as a large unsigned int, expected to exceed the length
// of the string. Passing the string length is functionally equivalent.
n = string.length;
}
return string.substring(pos, pos + n);
}
function assertSubstr(string, pos, n) {
assert.eq(expectedSubstr(string, pos, n), substr(string, pos, n));
}
function checkVariousSubstrings(string) {
for (pos = 0; pos < 5; ++pos) {
for (n = -2; n < 7; ++n) {
assertSubstr(string, pos, n);
}
}
}
checkVariousSubstrings("abc");
checkVariousSubstrings("");
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