Mutate F# [] Record
This code shows how to make a function mutate its input - one of the things we come to F# to avoid.
type Age = mutable n : int
let printInside a = printfn "Inside = %d" a.n
let inside a =
a.n <- a.n + 1
a.n
let a = n = 1
printInside a //a = 1
inside a
printInside a //a = 2
That being said, how do I do the same bad thing with [<Struct>] Records? I suspect that ref or byref may be involved but I just can't seem to get it to work.
type [<Struct>] Age = mutable n : int
let printInside a = printfn "Inside = %d" a.n
let inside a =
a.n <- a.n + 1
a.n
let a = n = 1
printInside a //a = 1
inside a
printInside a //a = 2
struct f# record
asked Nov 10 at 2:54
Brett Rowberry
18510
add a comment |
This code shows how to make a function mutate its input - one of the things we come to F# to avoid.
type Age = mutable n : int
let printInside a = printfn "Inside = %d" a.n
let inside a =
a.n <- a.n + 1
a.n
let a = n = 1
printInside a //a = 1
inside a
printInside a //a = 2
That being said, how do I do the same bad thing with [<Struct>] Records? I suspect that ref or byref may be involved but I just can't seem to get it to work.
type [<Struct>] Age = mutable n : int
let printInside a = printfn "Inside = %d" a.n
let inside a =
a.n <- a.n + 1
a.n
let a = n = 1
printInside a //a = 1
inside a
printInside a //a = 2
struct f# record
asked Nov 10 at 2:54
Brett Rowberry
18510
add a comment |
This code shows how to make a function mutate its input - one of the things we come to F# to avoid.
type Age = mutable n : int
let printInside a = printfn "Inside = %d" a.n
let inside a =
a.n <- a.n + 1
a.n
let a = n = 1
printInside a //a = 1
inside a
printInside a //a = 2
That being said, how do I do the same bad thing with [<Struct>] Records? I suspect that ref or byref may be involved but I just can't seem to get it to work.
type [<Struct>] Age = mutable n : int
let printInside a = printfn "Inside = %d" a.n
let inside a =
a.n <- a.n + 1
a.n
let a = n = 1
printInside a //a = 1
inside a
printInside a //a = 2
struct f# record
asked Nov 10 at 2:54
Brett Rowberry
18510
This code shows how to make a function mutate its input - one of the things we come to F# to avoid.
type Age = mutable n : int
let printInside a = printfn "Inside = %d" a.n
let inside a =
a.n <- a.n + 1
a.n
let a = n = 1
printInside a //a = 1
inside a
printInside a //a = 2
That being said, how do I do the same bad thing with [<Struct>] Records? I suspect that ref or byref may be involved but I just can't seem to get it to work.
type [<Struct>] Age = mutable n : int
let printInside a = printfn "Inside = %d" a.n
let inside a =
a.n <- a.n + 1
a.n
let a = n = 1
printInside a //a = 1
inside a
printInside a //a = 2
struct f# record
struct f# record
asked Nov 10 at 2:54
Brett Rowberry
18510
asked Nov 10 at 2:54
Brett Rowberry
18510
edited Nov 10 at 20:46
asked Nov 10 at 2:54
Brett Rowberry
18510
asked Nov 10 at 2:54
Brett Rowberry
18510
asked Nov 10 at 2:54
Brett Rowberry
18510
18510
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
The fundamental issue is that a mutable field can only be modified if the struct itself is mutable. As you noted, we need to use byref in the declaration of Age. We also need to make sure a is mutable and lastly we need to use the & operator when calling the function inside. The & is the way to call a function with a byref parameter.
type [<Struct>] Age = mutable n : int
let printInside a = printfn "Inside = %d" a.n
let inside (a : Age byref) =
a.n <- a.n + 1
a.n
let mutable a = n = 1
printInside a //a = 1
inside &a
printInside a //a = 2
answered Nov 10 at 6:37
Ringil
3,44021025
add a comment |
Now that I get the pattern, here is a simple example (just an int instead of a struct record) of how to mutate values passed into a function:
let mutable a = 1
let mutate (a : byref<_>) = a <- a + 1
mutate &a
a //a = 2
answered Nov 10 at 17:32
Brett Rowberry
18510
add a comment |
Your Answer
StackExchange.ifUsing("editor", function ()
StackExchange.using("externalEditor", function ()
StackExchange.using("snippets", function ()
StackExchange.snippets.init();
);
);
, "code-snippets");
StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "1"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);
else
createEditor();
);
function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader:
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
,
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);
);
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53235635%2fmutate-f-struct-record%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
The fundamental issue is that a mutable field can only be modified if the struct itself is mutable. As you noted, we need to use byref in the declaration of Age. We also need to make sure a is mutable and lastly we need to use the & operator when calling the function inside. The & is the way to call a function with a byref parameter.
type [<Struct>] Age = mutable n : int
let printInside a = printfn "Inside = %d" a.n
let inside (a : Age byref) =
a.n <- a.n + 1
a.n
let mutable a = n = 1
printInside a //a = 1
inside &a
printInside a //a = 2
answered Nov 10 at 6:37
Ringil
3,44021025
add a comment |
The fundamental issue is that a mutable field can only be modified if the struct itself is mutable. As you noted, we need to use byref in the declaration of Age. We also need to make sure a is mutable and lastly we need to use the & operator when calling the function inside. The & is the way to call a function with a byref parameter.
type [<Struct>] Age = mutable n : int
let printInside a = printfn "Inside = %d" a.n
let inside (a : Age byref) =
a.n <- a.n + 1
a.n
let mutable a = n = 1
printInside a //a = 1
inside &a
printInside a //a = 2
answered Nov 10 at 6:37
Ringil
3,44021025
add a comment |
The fundamental issue is that a mutable field can only be modified if the struct itself is mutable. As you noted, we need to use byref in the declaration of Age. We also need to make sure a is mutable and lastly we need to use the & operator when calling the function inside. The & is the way to call a function with a byref parameter.
type [<Struct>] Age = mutable n : int
let printInside a = printfn "Inside = %d" a.n
let inside (a : Age byref) =
a.n <- a.n + 1
a.n
let mutable a = n = 1
printInside a //a = 1
inside &a
printInside a //a = 2
answered Nov 10 at 6:37
Ringil
3,44021025
The fundamental issue is that a mutable field can only be modified if the struct itself is mutable. As you noted, we need to use byref in the declaration of Age. We also need to make sure a is mutable and lastly we need to use the & operator when calling the function inside. The & is the way to call a function with a byref parameter.
type [<Struct>] Age = mutable n : int
let printInside a = printfn "Inside = %d" a.n
let inside (a : Age byref) =
a.n <- a.n + 1
a.n
let mutable a = n = 1
printInside a //a = 1
inside &a
printInside a //a = 2
answered Nov 10 at 6:37
Ringil
3,44021025
answered Nov 10 at 6:37
Ringil
3,44021025
answered Nov 10 at 6:37
Ringil
3,44021025
answered Nov 10 at 6:37
Ringil
3,44021025
3,44021025
add a comment |
add a comment |
Now that I get the pattern, here is a simple example (just an int instead of a struct record) of how to mutate values passed into a function:
let mutable a = 1
let mutate (a : byref<_>) = a <- a + 1
mutate &a
a //a = 2
answered Nov 10 at 17:32
Brett Rowberry
18510
add a comment |
Now that I get the pattern, here is a simple example (just an int instead of a struct record) of how to mutate values passed into a function:
let mutable a = 1
let mutate (a : byref<_>) = a <- a + 1
mutate &a
a //a = 2
answered Nov 10 at 17:32
Brett Rowberry
18510
add a comment |
Now that I get the pattern, here is a simple example (just an int instead of a struct record) of how to mutate values passed into a function:
let mutable a = 1
let mutate (a : byref<_>) = a <- a + 1
mutate &a
a //a = 2
answered Nov 10 at 17:32
Brett Rowberry
18510
Now that I get the pattern, here is a simple example (just an int instead of a struct record) of how to mutate values passed into a function:
let mutable a = 1
let mutate (a : byref<_>) = a <- a + 1
mutate &a
a //a = 2
answered Nov 10 at 17:32
Brett Rowberry
18510
answered Nov 10 at 17:32
Brett Rowberry
18510
answered Nov 10 at 17:32
Brett Rowberry
18510
answered Nov 10 at 17:32
Brett Rowberry
18510
18510
add a comment |
add a comment |
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Some of your past answers have not been well-received, and you're in danger of being blocked from answering.
Please pay close attention to the following guidance:
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53235635%2fmutate-f-struct-record%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
