On 25/10/12 19:38, Brian Craft wrote:
Multimethods seem like a convenience layer over duck typing: probe the
object to see what it is, then dispatch. Is that a fair description?
Not exactly...MUlti-methods have no limitations with regarding dispatch.
You can dispatch on anything...I mean ANYTHING!!! To give you an idea,
my canva-react mulit-method dispatches on the type of game being played
at the moment which is not part of the parameters passed in!!! In other
words the dispatch function completely ignores the arguments! Nothing to
do with types/classes etc etc. You dispatch on some function - that is it!!!
similarly:
|(||defmulti||halt|
|(||fn||[||_ _||]| |;dispatch-function checks for OS - ignores args
|
|(||let||[||os||(||System/getProperty||"os.name"||)||]|
|||(||if||(||.startsWith os||"Mac OS"||)||:Linux
||(||keyword||os||)||)||)||)||)|
|;;for Linux and Mac machines |
|(||defmethod||halt :Linux||[||root-pwd minutes-after||]|
|||(||clojure||.java.shell/sh|
|||"sudo"||"-S"||"shutdown"||(||str||"+"||minutes-after||)||:in||(||str||root-pwd||"\n"||)||)||)|
|;;for Windows machines|
|(||defmethod||halt :Windows||[||_ minutes-after||]|
|||(||clojure||.java.shell/sh||"shutdown"||"-s"||"-t"|
|(||str||minutes-after||)||)||)|
|;;for Solaris machines|
|(||defmethod||halt :Solaris||[||root-pwd seconds-after||]|
|||(||clojure||.java.shell/sh|
|||"shutdown"||"-S"||"-y"||(||str||"-g"||seconds-after||)||"-i"||"S"||:in||(||str||root-pwd||"\n"||)||)||)|
|;;in case nothing fires|
|(||defmethod||halt||:default||[||]||(||throw||(||UnsupportedOperationException.||"Unsupported
operating system!"||)||)||)
Jim
|
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