# map.contains · Rell standard library · Chromia Docs (concept)

> pure function contains(key: K): boolean Check if this map contains the given key. Parameters key — the key to look up Returns true if this map contains the

Source: https://docs.chromia.com/pages/rell-stdlib/-rell-system-library/root/map/contains/

FUNCTION

# map.contains

```signature
pure function contains(key: K): boolean
```

Check if this map contains the given key.

**Parameters**

* **key** — the key to look up

**Returns**

`true` if this map contains the given key, `false` otherwise

Since 0.6.0

[View this page on docs.chromia.com](https://docs.chromia.com/pages/rell-stdlib/-rell%20-system%20-library/%5Broot%5D/map/contains.html)Generated API reference, mirrored from the live docs