Description:

The reader macro installed by enable-objective-c-syntax closely resembles the conventional method call syntax of Objective-C. In fact, any differences between standard Objective-C method call syntax and this reader macro that are not documented here are probably bugs and should be reported to the maintainer.

Reader Macro:

[{receiver | class-name}} message-name-part [[argument [[message-name-arg-pair]]&#42*]]]

message-name-arg-pair ::= message-name-part argument

Reader Macro Arguments and Values:

receiver --- an object.

class-name --- a symbol (not evaluated).

message-name-part --- a symbol (not evaluated).

argument --- an object.

Returns: result --- the result of the method invocation.

Reader Macro Description:

First, it is determined whether to regard the first element of the form as an object or as a class name according to the following rules:

1. If the element is no symbol, it is regarded as an object.

2. Otherwise, if it is a symbol whose name starts with a lowercase letter, it is regarded as an object.

3. Otherwise, it is regarded as a class name.

Next, the method call is parsed by alternately reading message name parts and arguments separated by whitespace. Message name parts are expected to consist of alphanumeric characters and colons, while arguments may be arbitrary Lisp expressions. If any but the first message name part does not end with a colon, the effects are undefined. Likewise, the effects are undefined if any message name part contains a colon in a position other than the end.

After the parsing is done, all message name parts are concatenated in order to form a single string that is used as if as the second argument to invoke-by-name, and all arguments are collected in order and the resulting list used as if as a list of additional arguments to invoke-by-name.

Reader Macro Examples:

[NSString stringWithCString: "Mulk."]  
  ;=> #<GSCBufferString `Mulk.' {5B36087}>  
  
[NSObject self]  
  ;=> #<NSObject `NSObject' {16ECF598}>  
  
[NSObject name]  
  ;=> "NSObject"  
  
[[[NSObject self] self] name]  
  ;=> "NSObject"  
  
[NSString stringWithCString: "Mulk." encoding: 4]  
  ;=> #<GSCBufferString `Mulk.' {5B36087}>  
  
 

Rationale:

Objective-C method names tend to be relatively verbose and are frequently composed of many short words like "of" and "by". As a result, using invoke can be quite cumbersome at times and waste screen real estate. One need only compare the example call

(invoke (find-objc-class 'ns-string)  
        :string-with-c-string "Mulk."  
        :encoding 4) 

with its reader macro counterpart

[NSString stringWithCString: "Mulk." encoding: 4] 

to be able to see an improvement in length as well as readability.

In any case, it is a matter of taste whether to prefer invoke or Objective-C syntax as it is whether to prefer the standard Common Lisp loop facility or a widespread and well-known alternative called "Iterate". In both cases, one can argue that one of the forms sacrifices an elusive quality of "lispiness" as well as text editor friendliness in favor of natural-language-style readability and conciseness.

See also:

invoke, invoke-by-name, disable-objective-c-syntax, enable-method-syntax