C#•2mo ago

Using ref for large data types.

Hi, just looking for a little clarification on the ref keyword when passing data into a function. I've hot an API endpoint which takes in files which passes them though to a function which checks them and sorts them into an appropriate destination directory. I've got a function in another class which checks the data type is supported, among other things. Would I be right to pass the incoming multipart File data to it using a ref value to avoid making a copy of it? Some of the files can run up to 200mb in size. Thanks for any help.

6 Replies

exe•2mo ago

If you pass in your File class, whatever it's called or contains, you pass the reference to it not a copy. So no need to use ref here.

DannyRoastBeef㊙•2mo ago

Hi thanks for the reply. What about if I was to pass a list containing incoming data as I am here in my GET endpoint?

[HttpPost]
        [Route("upload")]
        public async Task<IActionResult> UploadDataAsync(List<IFormFile>? files)
        {
            if (files is not null && _env is not null)
            {
               return await _checkpoint.SaveDataToStorage(files);
            }
            return new StatusCodeResult(400);
        }

[HttpPost]
        [Route("upload")]
        public async Task<IActionResult> UploadDataAsync(List<IFormFile>? files)
        {
            if (files is not null && _env is not null)
            {
               return await _checkpoint.SaveDataToStorage(files);
            }
            return new StatusCodeResult(400);
        }

In the following function I've got

public async Task<IActionResult> SaveDataToStorage(List<IFormFile> files)
        {
            List<IFormFile> incomingFiles = files;
            
            if (!CheckValidFileTypes(incomingFiles))
            {
                return new UnsupportedMediaTypeResult();
              (There's more going on in here , shortened it for this post)
            }
        }

public async Task<IActionResult> SaveDataToStorage(List<IFormFile> files)
        {
            List<IFormFile> incomingFiles = files;
            
            if (!CheckValidFileTypes(incomingFiles))
            {
                return new UnsupportedMediaTypeResult();
              (There's more going on in here , shortened it for this post)
            }
        }

Would it be correct to put ref in front of

incomingFiles

incomingFiles

when calling the

CheckValidTypes

CheckValidTypes

function or will that do a copy?

exe•2mo ago

There may be some intricacies which I've forgotten around the reference pointer on reference types using the ref keyword but the object is still the same object ASFAIK a list just contains a copy of the reference not the actual object. Meaning if you change something something on an object inside SaveDataToStorage you'll see the same changes when you step outside in files. You can confirm this quite easily I would not. Confirm that by making a change to one of the files in the list inside CheckValidFileTypes and step outside back into the SaveDataToStorage method, and the change is still reflected. You'll know then that no copies are made and it just passes around references Short answer: use-case for ref is actually quite limited

DannyRoastBeef㊙•2mo ago

Right! Thanks for your help with a succinct answer and explanation. I was getting sick of trying to decipher the correct approach from StackOverflow :blobthumbsup:

exe•2mo ago

No worries, good luck 🙂

Jimmacle•2mo ago

unless the types you're passing in are structs they're already passed as a reference instead of a copy

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Using ref for large data types.