# Coercion

Structure does type coercion based on the declared [schema](/schema-concept.md), let's break it into 3 categories:

* [Primitive type coercion](/coercion/primitive-type-coercion.md)
* [Arrays coercion](/coercion/arrays-and-array-subclasses.md)
* [Generic coercion](/coercion/generic-coercion.md)

## Observations

Structure **never** coerces the following scenarios:

* value is `undefined`;
* value is `null` when `nullable` option is enabled;
* value is already of the declared type (except for arrays, we'll talk more about this soon).


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