C#•2y ago

❔ IEnumerable and dependency injection

if i want to loop enumerable from DI multiple times

var foos = services.GetRequiredService<IEnumerable<Foo>>(); // add .ToList()?
foreach(foo in foos) {}
foreach(foo in foos) {}
foreach(foo in foos) {}

var foos = services.GetRequiredService<IEnumerable<Foo>>(); // add .ToList()?
foreach(foo in foos) {}
foreach(foo in foos) {}
foreach(foo in foos) {}

is it better to first get list? My concern is that DI will look for "Foo" multiple times even if it isn't needed

14 Replies

David_F•2y ago

The main point is that you should assume that it may iterate each time, so if you don't want that, then call .ToArray() on it the first time and cache it

Thinker•2y ago

You should pretty much always use ToList or ToArray when iterating an IEnumerable multiple times catsip

CrosRoad95OP•2y ago

thats a good point

David_F•2y ago

Depend on the contract, not on the current behavior IEnumerable contract is that it is lazily evaluated

CrosRoad95OP•2y ago

i know that if i have something what produces enumerable, and something what consumes it it should not make list or array out of it i imagine it as a some kind of pipelining ( IEnumerable )

Anton•2y ago

well, thing is, the DI container could already have cached it into an array (if the injection is not transient), so converting it a sceond time is just wasting memory, which is what the question is asking, I would assume need to look into the source code

David_F•2y ago

@CrosRoad95 Depends on the behavior you want to implement. If your subsequent pipeline processors need fresh data each time they enumerate, then yes, you should not cache it with ToArray()

Anton•2y ago

but consider that a microoptimization

CrosRoad95OP•2y ago

on the other hand, in my case i have very few elements and code that doing loop multiple is executed very rarely

Anton•2y ago

then you can just do it. it's gonna matter in behavior when there are transient dependencies so do call ToArray that's probably what you want what I mean is that with toarray the dependencies will be only created once, while without it it would create them on every loop lazily

Monsieur Wholesome•2y ago

Am I the only one baffled by the idea of storing some IEnumerable<int> in a service container

Anton•2y ago

they might've meant this https://learn.microsoft.com/en-us/dotnet/api/microsoft.extensions.dependencyinjection.serviceproviderserviceextensions.getservices?view=dotnet-plat-ext-7.0

ServiceProviderServiceExtensions.GetServices Method (Microsoft.Exte...

Get an enumeration of services of type serviceType from the IServiceProvider.

Unknown User•2y ago

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Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ IEnumerable and dependency injection