Changes between Version 151 and Version 152 of WebKitIDL


Ignore:
Timestamp:
Apr 24, 2016 6:17:04 PM (5 years ago)
Author:
Chris Dumez
Comment:

Drop [Default]

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  • WebKitIDL

    v151 v152  
    99[#IDLAttributes IDL attributes]
    1010 - [#TreatNullAs TreatNullAs(a,p)][[br]]
    11  - [#Default Default(p)][[br]]
    1211 - [#Clamp Clamp(a,p)][[br]]
    1312 - [#Custom Custom(m,a), CustomGetter(a), CustomSetter(a)][[br]]
     
    239238}}}
    240239
    241 == `[Default]`(p) == #Default
    242 
    243 Summary: `[Default]` allows specifying the default values for optional parameters to simplify WebCore implementations which otherwise require overloads.
    244 
    245 Standard: In Web IDL, `[Default=NullString]` is written as `"type identifier = default"`, e.g. `optional DOMString? str = null`
    246 
    247 Usage: The possible usages are `[Default=Undefined]` or `[Default=NullString]`. `[Default=Undefined]` can be specified on any optional parameter. `[Default=NullString]` can be specified on DOMString parameters only:
    248 
    249 {{{
    250     interface HTMLFoo {
    251         void func1(int a, int b, optional int c, optional int d);
    252         void func2(int a, int b, [Default=Undefined] optional int c);
    253         void func3(int a, int b, [Default=Undefined] optional DOMString c, [Default=NullString] optional DOMString d);
    254     };
    255 }}}
    256 
    257 The parameters marked with the standard Web IDL optional qualifier are optional, and JavaScript can omit the parameters. Obviously, if parameter X is marked with optional then all subsequent parameters of X should be marked with optional.
    258 
    259 The difference between optional and `[Default=Undefined]` optional is whether the WebCore implementation has overloaded methods or not, as explained below.
    260 
    261 In case of `func1(...)`, if JavaScript calls `func1(100, 200)`, then `HTMLFoo::func1(int a, int b)` is called in WebCore. If JavaScript calls `func1(100, 200, 300)`, then `HTMLFoo::func1(int a, int b, int c)` is called in WebCore. If JavaScript calls `func1(100, 200, 300, 400)`, then `HTMLFoo::func1(int a, int b, int c, int d)` is called in WebCore. In other words, if the WebCore implementation has overloaded methods, you can use optional.
    262 
    263 In case of `func2(...)` which adds `[Default=Undefined]`, if JavaScript calls `func2(100, 200)`, then it behaves as if JavaScript called `func2(100, 200, undefined)`. Consequently, `HTMLFoo::func2(int a, int b, int c)` is called in WebCore. 100 is passed to a, 200 is passed to b, and 0 is passed to c. (A JavaScript undefined is converted to 0, following the value conversion rule in the Web IDL spec.) In this way, WebCore needs to just implement `func2(int a, int b, int c)` and needs not to implement both `func2(int a, int b)` and `func2(int a, int b, int c)`.
    264 
    265 The difference between `[Default=Undefined]` and `[Default=NullString]` appears only when the parameter type is DOMString. In `[Default=Undefined]` the "supplemented" JavaScript undefined is converted to a WebKit string "undefined". On the other hand, in `[Default=NullString]` the "supplemented" JavaScript undefined is converted to a WebKit null string. For example, if JavaScript calls `func3(100, 200)`, then `HTMLFoo::func3(int a, int b, String c, String d)` is called in WebCore. At this point, 100 is passed to a, 200 is passed to b, a WebKit string "undefined" is passed to c, and a WebKit null string is passed to d. d.IsEmpty() and d.IsNull() return true.
    266 
    267240== `[Clamp]`(a,p) == #Clamp
    268241
     
    718691Whether you should allow an interface to have constructor depends on the spec of the interface.
    719692
    720 Note: Currently `[Constructor(...)]` does not yet support optional arguments w/o defaults. It just supports `[Default=Undefined] optional` or `[Default=NullString] optional`.
     693Note: Currently `[Constructor(...)]` does not yet support optional arguments w/o defaults.
    721694
    722695== `[ConstructorTemplate]`(i), `[InitializedByEventConstructor]`(a) == #ConstructorTemplate