rfc:union_types

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rfc:union_types [2016/06/14 14:35]
levim Rework grammar in Introduction 		rfc:union_types [2016/06/14 14:44]
levim
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 ===== Introduction ===== ===== Introduction =====
-Type declarations (function parameter and return types) perform two useful roles:+PHP has [[http://php.net/manual/en/functions.arguments.php#functions.arguments.type-declaration|type declarations]] which can be associated with function parameters or return values. These declarations perform two useful roles:
  
-  * Using types allows the PHP engine to enforce the correct type of variable passed to, or returned from, a function. +  * They allow the PHP engine to enforce the correct type of variable passed to or returned from a function. 
-  * Using types makes it easy to reason about what types need to be passed to, or can be returned from a function. This makes it easier for both humans, and static code analysis tools, to determine about whether code is correct or not.+  * They make it easier to reason about what types need to be passed to or can be returned from a function. Both humans and static code analysis tools can use this information to help determine the correctness of the code.
  
 For a lot of functions in PHP each parameter will only be one type. Similarly, for the majority of functions the return value will only ever be of one type. For a lot of functions in PHP each parameter will only be one type. Similarly, for the majority of functions the return value will only ever be of one type.
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 This RFC seeks to address these limitations. This RFC seeks to address these limitations.
  
-==== Proposal ====+===== Proposal =====
 This RFC proposes the ability to define multiple possible types for parameter and return types. To define a 'union type' a single vertical bar (OR) is placed between types e.g. ''int|bool'' represents the union type of either integer or boolean. For these 'union types' a value passes the type check if the value would pass any one of the types in the union.  This RFC proposes the ability to define multiple possible types for parameter and return types. To define a 'union type' a single vertical bar (OR) is placed between types e.g. ''int|bool'' represents the union type of either integer or boolean. For these 'union types' a value passes the type check if the value would pass any one of the types in the union. 
  
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 There can be more than two types in the union. There can be more than two types in the union.
  
-=== Parameter type examples ===+==== Parameter type examples ====
 A function that requires either a string or an array is passed to it as the parameter: A function that requires either a string or an array is passed to it as the parameter:
 <PHP> <PHP>
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 For this example, it is clear to both static analysis tools and humans that passing anything other than a ParameterGenerator object or a string to this function, would be an error.  For this example, it is clear to both static analysis tools and humans that passing anything other than a ParameterGenerator object or a string to this function, would be an error. 
  
-=== Return type example ===+==== Return type example ====
 A userland definition of ''stripos'' function: A userland definition of ''stripos'' function:
  
rfc/union_types.txt · Last modified: 2017/09/22 13:28 (external edit)

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