lambda expression function

Question

I have this code:

int pictureId=10;
string cacheKey = string.Format(ModelCacheEventConsumer.PICTURE_URL_MODEL_KEY, pictureId);
        return _cacheManager.Get(cacheKey, () =>
        {
            var url = _pictureService.GetPictureUrl(pictureId, showDefaultPicture: false);
            //little hack here. nulls aren't cacheable so set it to ""
            if (url == null)
                url = "";

            return url;
        });

What exactly this part of code means:"

() =>
{"
   var url =...."

Does it mean that function, which returns URL, is executed for every row from cache? What is then return type - list?

URL of documentation of this syntax?

_cacheManager implements ICacheManager IDisposable interface, which has method Get defined as: T Get(string key); — Simon, Jan 04 '16 at 20:29

GregC · Answer 1 · 2016-01-04T21:08:00.007

Second parameter to _cacheManager.Get() method is an anonymous method that captures pictureId and among other things.

https://msdn.microsoft.com/en-us/library/bb397687.aspx

C# Lambda expressions: Why should I use them?

To figure out the returned type, try using var keyword and creating a local variable: instead of return _cacheManager.Get() write var x = _cacheManager.Get() followed by return x. Then simply hover over the keyword var in Visual Studio.

fabriciorissetto · Answer 2 · 2016-01-04T20:03:20.560

1

What exactly this part of code means

It's just passing a method by parameter.

Does it mean that function, which returns URL, is executed for every row from cache?

Only the content of the method Get of the object _cacheManager can answer this.

What is then return type - list?

The return type is a string, since your variable url is a string.

edited Jan 04 '16 at 20:03

answered Jan 04 '16 at 19:57

fabriciorissetto

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Sorry, i mean what type is variable returned from Get method, like list of strings or array of strings.. – Simon Jan 04 '16 at 20:32
1

@Simon its only possible to answer it looking inside the method Get or passing the mouse over the method (if you're using Visual Studio). The return type will be shown for you – fabriciorissetto Jan 05 '16 at 12:12

score 1 · Answer 3 · answered Jan 04 '16 at 20:11

What exactly this part of code means:

Well, lambda expression is a "shortcut" for delegate, and delegate is a reference to a callback function (in a very simple explanation). So this is a function which will be called inside your Get method of cache manager, which expects to have a Func delegate as a second param

Does it mean that function, which returns URL, is executed for every row from cache?

I think it will executes for row which has a key value the same as the value of cacheKey variable.. So, only one time (if keys are unique)

What is then return type - list?

The return type is string, because if result of GetPictureUrl is null it returns empty string. And calling this method is expecting to have a string in a result also

lambda expression function

3 Answers3