Can I insert into a map by key in F#? -


i'm messing around bit f# , i'm not quite sure if i'm doing correctly. in c# done idictionary or similar.

type school() =    member val roster = map.empty get, set     member this.add(grade: int, studentname: string) =       match this.roster.containskey(grade)         | true -> // can this.roster.[grade].insert([studentname])?         | false -> this.roster <- this.roster.add(grade, [studentname])

is there way insert map if contains specified key or using wrong collection in case?

the f# map type mapping keys values ordinary .net dictionary, except immutable.

if understand aim correctly, you're trying keep list of students each grade. type in case map integers lists of names, i.e. map<int, string list>.

the add operation on map either adds or replaces element, think that's operation want in false case. in true case, need current list, append new student , replace existing record. 1 way write like:

type school() =    member val roster = map.empty get, set     member this.add(grade: int, studentname: string) =      // try current list of students given 'grade'      let studentsopt = this.roster.tryfind(grade)       // if result 'none', use empty list default       let students = defaultarg studentsopt []      // create new list new student @ front      let newstudents = studentname::students      // create & save map new/replaced mapping 'grade'      this.roster <- this.roster.add(grade, newstudents)

this not thread-safe (because calling add concurrently might not update map properly). however, can access school.roster @ time, iterate on (or share references it) safely, because immutable structure. however, if not care that, using standard dictionary fine - depends on actual use case.


Comments

Post a Comment

Popular posts from this blog

commonjs - How to write a typescript definition file for a node module that exports a function? -

consider, toml node module can use: // toml.d.ts declare module toml { export function parse(value:string):any; } declare module "toml" { export = toml; } then: /// <reference path="../../../../../defs/toml/toml.d.ts"/> import toml = require('toml'); toml.parse(...); however, node module export single function, such 'glob' ( https://github.com/isaacs/node-glob ). the node usage of module be: var glob = require("glob") glob("*.js", {}, callback(err, files) { ... }); you'd naively expect this: // glob.d.ts declare function globs(paths:string, options:any, callback:{(err:any, files:string[]):void; ...but because typescripts 'import' semantics bit strange, seems can use 'import .. = require()' statement alias modules . trying call: /// <reference path="../../../../../defs/glob/glob.d.ts"/> import blog = require('glob'); results in: error ts2072: mod...
Read more

openid - Okta: Failed to get authorization code through API call -

i'm integrating okta own idp server using okta's api. i'm implementing authorization code flow following steps below: in own server, use /api/v1/authn endpoint sessiontoken. use sessiontoken obtain authorization calling endpoint: /oauth2/v1/authorize?client_id=" + clientid + "&sessiontoken=" + sessiontoken + "&response_type=code&response_mode=query&scope=openid&redirect_uri=" + redirecturl + "&state=evanyang&nonce=" it's supposed return response status code 302 , location header containing redirect url code value. however, keep getting response status code 200 , without location header, html body saying "you using unsupported browser." , "javascript disabled on browser." according api documentation: http://developer.okta.com/docs/api/resources/oidc.html#authentication-request , sessiontoken parameter sufficient this: an okta one-time sessiontoken. allows api-based ...
Read more

ios - Change Storyboard View using Seague -

i have following code checks connection server, , depending on want change views if no connection found. nsstring *connect = [nsstring stringwithcontentsofurl:[nsurl urlwithstring:@"http://myserver.com"] encoding:nsutf8stringencoding error:nil]; if (connect == null) { [self performseguewithidentifier:@"network_failure" sender:self]; } else { // other code here } my problem not change views. have added storyboard segue between 2 views identifier of network_failure . not have navigation controller or that, problem? thanks help! no not problem. first of all, in objectivec exists nil object oriented null . must use that. so: if(connect == nil) or better: if(!connect) so due fact nil not same of null , probably code does't enter in if scope . you have been able discover breakpoint. anyway: be sure set trigger segue (line) 2 view controller , , name network_failure (that not best name. should instead view1toview2 ) as, m...
Read more