On 24/02/11 8:33 AM, Stas Malyshev wrote:
Hi!
use the function: you would usually be expected to pass in a true enum
constant of the MyEnum type.
That works wonders in dynamic languages, without any means of really
ensuring it.
No, I believe you can ensure it, and you can even ensure it efficiently.
I don't see how you can do it without typing variables and functions
and doing static type control.
You can do it like this. When an enum is defined:
- internally create a class to represent the enum; flag it as an enum
class, not a regular class; this restricts any PHP code from
attempting to access properties of the class, instantiate it, etc..
- internally instantiate an object of the class for every enum constant;
each object contains a member with the integer/string representation
of the constant.
- internally create a static array in the class, associating every enum
value to its instantiated object.
When an enum is type-hinted, you just check the value is internally an
object of the enum class.
When cast to integer or string, or serialising, or used in a context
where an integer or string is required, simply use the scalar value in
the enum object. Perhaps do this whenever passed to a built-in function,
too, unless explicitly type-hinted, or a special case such as
call_user_func where the enum is going to work its way back into PHP
code, merely as a convenience to avoid needing to change a lot of C code
to check and cast enums.
When cast to enum, or deserialising, look up the relevant integer or
string in the internal enum class's array to efficiently get the
strongly typed enum value.
When comparing enums for equality, compare pointers only. There will
always be exactly one internal object for each enum constant, so this
will work.
When comparing enums for ordering (less than, greater than), look up the
scalar values and compare them.
Even then - what if you read values from config file or database?
Would you have 50-item switch to match config values to typed Enum
values?
You'd just cast it to the enum type, at which point PHP would look up
the enum value in the internal array in the enum class to efficiently
retrieve the relevant strongly typed enum constant.
I also suggest when type-hinting, if the type is integer or string where
an enum is expected, PHP attempts a cast before failing, to make this
more convenient.
Ben.
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