Overriding static properties in F# with extension methods -


f# extension methods can defined on types same name , type signature existing instance , static methods override default implementation of these methods, can't work on static properties.

in particular, i'm trying create extension method datetime returns more precise time follows:

#nowarn "51"  open system  module datetimeextensions =      open system.runtime.interopservices      [<dllimport("kernel32.dll", callingconvention = callingconvention.winapi)>]     extern void private getsystemtimepreciseasfiletime(int64*)      type system.datetime         // example showing static methods can overridden         static member isleapyear(_: datetime) =             printfn "using overridden isleapyear!"             true          // more accurate utcnow method (note: not supported older os versions)         static member utcnow =             printfn "using overridden utcnow!"             let mutable filetime = 0l             getsystemtimepreciseasfiletime(&&filetime)             datetime.fromfiletimeutc(filetime)

however, output when executing

open datetimeextensions let _ = datetime.isleapyear(datetime.utcnow)

is just

using overridden isleapyear!

which shows static method 'override' working, not static property.

(note: i'm using f# 4.0)

this statement seems incorrect:

f# extension methods can defined on types same name , type signature existing instance , static methods override default implementation of these methods, can't work on static properties.

no, don't override.

you might confused because in fact signature of isleapyear wrong, should take integer, that's why works mean not overriding anything, adding new (extension) method.

if try original signature you'll see doesn't work either:

type system.datetime     // example showing static methods can not overridden     static member isleapyear(_: int) =         printfn "using overridden isleapyear!"         false  > datetime.isleapyear(2000);; val : bool = true

which consistent behavior of static property extension.

anyway i'm not sure why decided not override, if there such decision @ when designing language. think interesting feature , if there reason not implement @ least should emit warning saying since method exists never called.

maybe open issue or suggestion f# compiler.


Comments

Post a Comment

Popular posts from this blog

php - Vagrant up error - Uncaught Reflection Exception: Class DOMDocument does not exist -

i've set bento/ubuntu-16.04 vagrant box using php 5.6, , getting following error quite few times when try , run shell script: "uncaught reflection exception: class domdocument not exist". i've tried adding following top of script (not together), each no success: "sudo apt-get install php5.6-xml", "sudo apt-get install php5-xml", "sudo apt-get install php-dom" i've tried resetting server "sudo service apache2 restart". does have suggestions?
Read more

vue.js - Create hooks for automated testing -

Image
qa guys complained can't automate frontend testing. because our html looks same outside. lazy hack did this <template> <div :role="$options.name"> ... </div> </template> <script> export default { name: 'vmcomponentname' } </script> which takes name script , applies html. in browser get: <div role="vmcomponentname"> ... </div> line :role="$options.name" goes in every component. is there dry er solutions? please share. additional details i'll explain in details looking for. imagine have vmusercreate form creates user. test case can create user . to automatically test without role, have use following selector: .wrapper > .wrapper > .wrapper > .submit-button the test extremely brittle (will break lot). if use roles can use [role="vmusercreateform"] .submit-button selector. many folds less brittle. so basically, i'm ...
Read more

Add new key value to json node in java -

i have json file : { "id":1, "name":"abc", "addressdetails": { "city":"newyork" } } i wanted add 1 more key-value ("pincode" : "414141") node 'addressdetails'. i tried using : objectmapper mapper = new objectmapper(); jsonnode root = mapper.readtree(new file("d://test.json")); objectnode node = mapper.createobjectnode(); node.with("addressdetails").put("pincode", "414141"); but it's not getting added, there way can ? you can try you should modify file path objectmapper mapper = new objectmapper(); objectnode nodes = mapper.readvalue(new file("d:\\test.txt"), objectnode.class); nodes.with("addressdetails").put("pincode", "414141"); mapper.writer().writevalue(new file("d:\\test.txt"), nodes);
Read more