C#•2y ago

✅ Explicit call ToString() when interpolating on primitive (value) types

Is it necessary to call ToString() when interpolating string using primitive (int, float, etc.) or in general value types? Would it avoid boxing allocation? Example:

int someInt = 4;
MyStructWithImplementedInterfaceIFormatable myStruct;
Console.Write($"My number is: {someInt.ToString()} and struct: {myStruct.ToString()}");

int someInt = 4;
MyStructWithImplementedInterfaceIFormatable myStruct;
Console.Write($"My number is: {someInt.ToString()} and struct: {myStruct.ToString()}");

18 Replies

ero•2y ago

Well first off this doesn't compile. But also, why not just try it?

MODiX•2y ago

Ero#1111

REPL Result: Success

int someInt = 4;

Console.WriteLine($"{someInt}");

int someInt = 4;

Console.WriteLine($"{someInt}");

Console Output

Compile: 606.991ms | Execution: 32.196ms | React with ❌ to remove this embed.

Ice_trooperOP•2y ago

What do you want to explain to me? ;p I know it would work, but the essence of the question is: should I call explicitlly ToString to avoid boxing allocation?

ero•2y ago

You asked 2 separate questions Not my fault

Ice_trooperOP•2y ago

Ok, I'm sorry. You're right that it could be understood this way 😅

ero•2y ago

Calling ToString on anything will allocate (a string), i dont think it would box?

Ice_trooperOP•2y ago

Yeah, but here I'm using value types

Thinker•2y ago

.ToString() is called implicitly when using string interpolation It will allocate a string regardless (I think)

Ice_trooperOP•2y ago

Yes, but on what type is it called implicitly? On int/MyStruct directly or is it boxing value type to object and then it will call ToString() (less efficient)?

Thinker•2y ago

The IL contains no boxing, although you might have to dig into the source of DefaultInterpolatedStringHandler.

MODiX•2y ago

thinker227#5176

sharplab.io (click here)

int a = 2;
int b = 7;
string s = $"The first number is {a} and the second number...
System.Console.WriteLine(s);

int a = 2;
int b = 7;
string s = $"The first number is {a} and the second number...
System.Console.WriteLine(s);

React with ❌ to remove this embed.

Ice_trooperOP•2y ago

Yeah, I also checked that it uses that handler, but I cannot find information how it behaves internally. :/

Thinker•2y ago

The source is here https://source.dot.net/#System.Private.CoreLib/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/DefaultInterpolatedStringHandler.cs,1aa9a7f847d81b2f It has some pretty extensive comments if you wanna read through it It appears that when formatting objects, it tries to format it using IFormattable, otherwise it calls ToString() on the type. However it's using a type argument, which means that no boxing is taking place.

MODiX•2y ago

Retax#0813

sharplab.io (click here)

System.Console.WriteLine($"{(new S()).ToString()}");
readonly struct S {}

System.Console.WriteLine($"{(new S()).ToString()}");
readonly struct S {}

React with ❌ to remove this embed.

Ice_trooperOP•2y ago

@🌈 Thinker 🌈 @Retax I was just reading links you pasted and articles about that. Do I understand correctly that since C#10 we got a concept of String Interpolation Handlers and it's optimized on that level so we don't have to explicitly call ToString() on value-types? https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/tutorials/interpolated-string-handler Unlike previous versions of C#, where string.Format was used when calling interpolation with int (without explicitly ToString() call). https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-10.0/improved-interpolated-strings#the-handler-pattern Last sum up question: Does it follow that up to C#10 version you should call ToString() yourself, but since this version they have improved it and DefaultInterpolatedStringHandler does it for us?

Ice_trooperOP•2y ago

I think I'm going to disagree with that. Can you justify it? As far as I can see in the latest version of C# we use a generic method that checks if the type implements the IFormatable interface. However, the old C# uses the string.Format(string, object) method, so he is already doing the boxing allocation at the stage of calling this method. Calling ToString() by itself gets rid of this.

Ice_trooperOP•2y ago

https://sharplab.io/#v2:EYLgZgpghgLgrgJwgZwLQBsD2BjK7VhwB22MAlpkarDAmcHDCgDQwhnrMAmIA1AD4ABAEwBGALAAoQQGYABCLkBhOQG8pczQvmCALHICyACgCUajVstkiMOQFsAngEkbcgLxzdAbguXNvv0FRAAY5AGtRdzkAEgAiAwc5azY1RxcYAF9Yn0k/LQCrV0cAZQhsSi50qIBWHLz/XPri2msAc3DhKLiEuWQyiqSbEFSHUvKiSpsAOgAVTGa6IlbTLLqtDKkMoA= Thank you 😄

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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✅ Explicit call ToString() when interpolating on primitive (value) types