Which data structure allows you to access values using both keys and indexes?

The correct choice is a Map, which is a data structure that allows you to store key-value pairs and access values using their associated keys. This means that you can retrieve a value directly by referencing its key, which is particularly useful for quick lookups in a collection of data.

Additionally, while a Map typically allows for key-based access, it does not inherently provide index-based access like an Array does. An Array enables access through numeric indexes, so although it is efficient for accessing items in a sequential manner, it does not involve key-value pairs.

On the other hand, a Dictionary is quite similar to a Map in certain programming languages, as it primarily focuses on key-value pairs as well. However, the terminologies and implementations might differ based on the language context, leading to potential ambiguity.

Lastly, a Variant is not a commonly recognized structure for the dual access (by keys and indexes) within the context provided. Instead, a Variant often refers to a type that can hold different data types, lacking the specific key-value structure that a Map offers.

Thus, the Map stands out as the best choice for its ability to efficiently provide access to values through keys and ultimately reflects the characteristics outlined in the question.