Initial implementation of IFormattable

[tmilnthorp]

Fixes #579

Initial go at #579. Didn't get much input there, so see if we like it!

[tmilnthorp]

While working on this I realized... any reason we use GlobalConfiguration.DefaultCulture for everything? Why not just use CultureInfo.CurrentCulture? I think that is more what a user would expect. If you changed CurrentCulture right now, you'd also have to change the GlobalConfiguration.DefaultCulture for it to be picked up.

[angularsen]

Hm, good point. I don't really see a good reason to keep it, I don't see what it gives us.

To add to it, there is the distinction of CultureInfo.CurrentCulture and CultureInfo.CurrentUICulture and I think we only have a configuration for the latter. If I recall correctly, the guidelines say something along the lines of

• CurrentUICulture for translations/localizations
• CurrentCulture for number formatting

It's probably more nuanced than that, but that's how I remember it. I think you have to manipulate CultureInfo.CurrentCulture to change the default number formatting used by ToString(). If that is correct, then what you propose would be more consistent too. It's a breaking change though, so something to add to #563 .

[angularsen]

I'll review the PR later.

[tmilnthorp]

I re-merged with after the script split. I'm curious your thoughts!

[tmilnthorp]

Looking at the standard format strings for:

• Numeric types
• DateTime

It seems that they use case insensitivity for the default format strings.

Custom format strings tends to be case sensitive though. Should we follow a similar paradigm? What denotes a custom format vs standard though is what we should probably figure out! 😃

[angularsen]

Maybe support significant digits after radix point here? Mass.FromKilograms(15.3).ToString("V4") could output 15.3000 similar to 15.3.ToString(F4) would.

[angularsen]

In the same spirit V#### could maybe output 15.3, similar to how 15.3.ToString("0.####") would. # is used to represent up to N numbers, but omit any trailing zeros when used after radix point.

[tmilnthorp]

That's what S does (must be given a number). You want both to do the same thing?

[tmilnthorp]

I always wonder at what point do we stop with the strings and let the user just do a string.format("0.####", quantity.Value) ❓

[angularsen]

Fair points, I've had the same thought.
Doesn't S also include the abbreviation? Maybe I read it wrong.

[angularsen]

Length.FromCentimeters(15.34000).ToString(null, 5) => 15.34 cm, so yes, it does the # thing.

So my proposal would be:
Length.FromCentimeters(15.34000).ToString("V####") to get 15.34 without the unit abbreviation.

It's valid on its own, but I agree with you, at some point people should just do standard/custom numeric formatting of the Value property. I can agree to don't do the V#### usecase on that ground.

[angularsen]

It seems that they use case insensitivity for the default format strings.

Actually, it seems to me they are in fact different.

"g" short time vs "G" long time.

Same for "d"/"D", "f"/"F", "t"/"T", "u"/"U" differing on short/long or short/full formats.
These are all standard formats and that to me adds weight to the argument to keep it all case sensitive - to avoid any confusion. For instance "o" and "O" are identical in Date, which to me just adds confusion when most other standard formats have different outputs for lower and upper case.

What denotes a custom format vs standard though is what we should probably figure out! 😃

From Date docs:

Any date and time format string that contains more than one character, including white space, is interpreted as a custom date and time format string; for more information, see Custom Date and Time Format Strings.

The numeric docs say pretty much the same thing, except the also accept an optional number xx behind the letter.

The way I read it, "standard" here only means their vetted, recommended, typical formats. The formats they want the .NET ecosystem to use. While custom is anything else, with a combination of date and time parts as well as free text fashioned together in any way you like.

In our case, I'm thinking standard format specifiers could maybe be like this:

• g: 15.1 kg
• s4: 15.1000 kg
• S4: 15.1 kg (using # to omit trailing zeros)

Custom format specifiers:

• a: kg
• a2: (2nd abbreviation for kilogram, or empty string(?) if not exists)
• q: Mass
• u: Kilogram
• v: 15.1
• v4: 15.1000
• v####: 15.1

Then later, if we add human readable strings, we could add

• Q: Bit Rate
• U: Bit per Second
• P or Up: Bits per Second

Update: On second thought, maybe human readable strings should be the lowercase format specifiers to hint at them being the preferred format specifiers, while enum names for quantity and unit as uppercase specifiers to hint at them being the secondary choice.

[tmilnthorp]

You're right... I think I'm going crazy 🤡 I've had a sick baby at home and not much sleep 😆

I'll make them lower-case for now.

[angularsen]

I can relate :-D a solid case of the chickenpox the past two days here reaching its peak just about now :-)

[angularsen]

I think with your latest changes, this is getting ready to merge. We don't need to get this perfect on the first try, let's just try something and see how it feels. We can leave v4 and v#### out for now.

[tmilnthorp]

Oh man. Hope everything's better!

I've added doc about the valid format strings.

Also, I think we should obsolete the following methods as part of this PR:

• public string ToString([CanBeNull] IFormatProvider provider)
  • Use ToString("g", provider)
• public string ToString([CanBeNull] IFormatProvider provider, int significantDigitsAfterRadix)
  • Use ToString("s2", provider) (or however many digits in format string)
• public string ToString([CanBeNull] IFormatProvider provider, [NotNull] string format, [NotNull] params object[] args)
  • Use string.format using value, unit, etc.

[angularsen]

Looks nice! Some feedback.

I also, I think we should obsolete the following methods as part of this PR:

Sounds good to me.

[angularsen]

More feedback :-) This should be getting ready to merge.

[angularsen]

Just a little bit more :-)

[angularsen]

You also have a bit of merge conflicts to deal with ;-) Fortunately almost all of them are just regens.

[tmilnthorp]

Merged and updated. I think it's done! 🎉

[angularsen]

Wohoo :) Awesome job on this!

[MrFoged]

Could you give a little insight into how to use the new string.Format?

Right now i have this code:
.ToString(new CultureInfo("en-US"), "{0:N1} {1}") which it tells me to change but to what? :-)

[tmilnthorp]

The equivalent of that should be:

string.Format(new CultureInfo("en-US"), "{0:N1} {1:a}", quantity.Value, quantity);

[angularsen]

Updated docs in String Formatting · angularsen/UnitsNet Wiki