langref.org - fsharp, fantom, and go - Maps

Check if a key exists in a map

Given a map pets {joe:cat,mary:turtle,bill:canary} print "ok" if an pet exists for "mary"

fsharp

if (Map.mem "mary" pets) then printfn "ok"

if pets.ContainsKey("mary") then printfn "ok"

fantom

map := ["joe":"cat", "mary":"turtle", "bill":"canary"]
if (map.containsKey("mary")) echo("ok")

go

m := map[string]string{ "joe": "cat", "mary": "turtle", "bill": "canary" }
if _, ok := m["mary"]; ok {
fmt.Println("ok")
}

Retrieve a value from a map

Given a map pets {joe:cat,mary:turtle,bill:canary} print the pet for "joe" ("cat")

fsharp

if (Map.mem "joe" pets) then printfn "%s" (Map.find "joe" pets)

if (pets |> Map.exists (fun key _ -> key = "joe")) then printfn "%s" (Map.find "joe" pets)

let key = "joe"
match (pets |> Map.tryfind key) with
| Some(value) -> printfn "%s" value
| None -> printfn "Key %s not found" key

if pets.ContainsKey("joe") then printfn "%s" pets.["joe"]

if pets.ContainsKey("joe") then printfn "%s" (pets.["joe"] :?> string)

fantom

map := ["joe":"cat", "mary":"turtle", "bill":"canary"]
pet := map["joe"]
echo("pet=$pet")

go

fmt.Println(pets["joe"])

Add an entry to a map

Given an empty pets map, add the mapping from "rob" to "dog"

fsharp

pets <- (Map.add "rob" "dog" pets)

pets.Add("rob", "dog")

fantom

map["rob"] = "dog"

go

pets["rob"] = "dog"

Remove an entry from a map

Given a map pets {joe:cat,mary:turtle,bill:canary} remove the mapping for "bill" and print "canary"

fsharp

let key = "bill"
match (pets |> Map.tryFind key) with
| Some(value) -> pets <- (Map.remove key pets) ; printfn "%s : %s removed" key value
| None -> printfn "Key %s not found" key

let key = "bill"
let entry = if (pets.ContainsKey(key)) then Some(pets.[key]) ; else None
pets.Remove(key)

match entry with
| Some(value) -> printfn "%s" value
| None -> printfn "key not found"

fantom

pet := map.remove("bill")
echo ("pet=$pet")

go

fmt.Println(pets["bill"])
delete(pets, "bill")

fmt.Println(pets["bill"])
pets["bill"] = "", false