// SERVER-18222: Add $isArray aggregation expression.
let coll = db.is_array_expr;
coll.drop();

// Non-array types.
assert.commandWorked(coll.insert({_id: 0, x: 0}));
assert.commandWorked(coll.insert({_id: 1, x: "0"}));
assert.commandWorked(coll.insert({_id: 2, x: new ObjectId()}));
assert.commandWorked(coll.insert({_id: 3, x: new NumberLong(0)}));
assert.commandWorked(coll.insert({_id: 4, x: {y: []}}));
assert.commandWorked(coll.insert({_id: 5, x: null}));
assert.commandWorked(coll.insert({_id: 6, x: NaN}));
assert.commandWorked(coll.insert({_id: 7, x: undefined}));

// Array types.
assert.commandWorked(coll.insert({_id: 8, x: []}));
assert.commandWorked(coll.insert({_id: 9, x: [0]}));
assert.commandWorked(coll.insert({_id: 10, x: ["0"]}));

// Project field is_array to represent whether the field x was an array.
let results = coll.aggregate([{$sort: {_id: 1}}, {$project: {isArray: {$isArray: "$x"}}}]).toArray();
let expectedResults = [
    {_id: 0, isArray: false},
    {_id: 1, isArray: false},
    {_id: 2, isArray: false},
    {_id: 3, isArray: false},
    {_id: 4, isArray: false},
    {_id: 5, isArray: false},
    {_id: 6, isArray: false},
    {_id: 7, isArray: false},
    {_id: 8, isArray: true},
    {_id: 9, isArray: true},
    {_id: 10, isArray: true},
];

assert.eq(results, expectedResults);