[Destructively] modifies the item specified by the
indexes to the value.
| item-at! < metabang.cl-containers:alist-container > < t > |
| item-at! < array > < t > |
| item-at! < metabang.cl-containers:array-container > < t > |
| item-at! < metabang.cl-containers::associative-array > < t > |
| item-at! < metabang.cl-containers:associative-container > < t > |
| item-at! :before < metabang.cl-containers:flexible-vector-container > < t > |
| item-at! :around < metabang.cl-containers:keyed-associative-container > < t > |
| item-at! < metabang.cl-containers:ring-buffer > < t > |
| item-at! < metabang.cl-containers:simple-associative-container > < t > |
| item-at! < metabang.cl-containers:sparse-array-container > < t > |
| item-at! < metabang.cl-containers:stable-associative-container > < t > |
| item-at! < t > < hash-table > |
| item-at! < metabang.cl-containers::vector-container-mixin > < t > |