rc-js-util/docs/rc-js-util.mapconcat_1.md

A collection of TS and C++ utilities to help writing performant and correct applications, achieved through strict typing and (removable) invariant checking.

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## mapConcat() function

Used with maps that store arrays. Where an array exists for a given key the values will be appended to that array, otherwise a copy of values array will be inserted.

**Signature:**

```typescript
export declare function mapConcat<TKey extends object, TValue>(map: WeakMap<TKey, TValue[]>, key: TKey, values: readonly TValue[]): void;
```

## Parameters

<table><thead><tr><th>

Parameter


</th><th>

Type


</th><th>

Description


</th></tr></thead>
<tbody><tr><td>

map


</td><td>

WeakMap&lt;TKey, TValue\[\]&gt;


</td><td>

The `Map` to check. May be modified.


</td></tr>
<tr><td>

key


</td><td>

TKey


</td><td>

The key to lookup in `map`<!-- -->.


</td></tr>
<tr><td>

values


</td><td>

readonly TValue\[\]


</td><td>

The values to concat.


</td></tr>
</tbody></table>
**Returns:**

void

## Remarks

See [mapConcat()](./rc-js-util.mapconcat.md)<!-- -->.