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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 ] } } } ).result[ 0 ].a;
}
function expectedSubstr( string, pos, n ) {
if ( pos < 0 ) {
// A negative value is interpreted as a large unsigned int, and is expected to be out of
// bounds.
return "";
}
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 = -2; pos < 5; ++pos ) {
for( n = -2; n < 7; ++n ) {
assertSubstr( string, pos, n );
}
}
}
checkVariousSubstrings( "abc" );
checkVariousSubstrings( "" );
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