truncateAsFixed() idea

[shmink]

Hello, I ran into an issue today at work (using flutter at work) where I was receiving a double from the backend that was 116.41666666. I wanted to display this value as an amount of money, such as £116.41 and I didn't expect any rounding to occur.

Unfortunately, I found out that toStringAsFixed() does appear to round as I was getting £116.42 on the display. I searched but I didn't see any kind of way to effectively truncate a double to a fixed amount.

In the end, I created a function to do it for me. I don't think it's great but maybe a jumping-off point for a feature that I think would be useful to have in the SDK.

https://dartpad.dev/?id=e8ab76b086cbd79b212491b38bf58a7f

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Only now of writing this do I see on the docs the example line toStringAsFixed()

(4321.12345678).toStringAsFixed(5);  // 4321.12346

where it shows rounding but my personal opinion is that it's not obvious enough. Perhaps instead

(1.118).toStringAsFixed(2);  // 1.12

maybe it's the 1, 2, 3, ... it doesn't stand out.

Either way, kind regards, Tom.

[dart-github-bot]

Labels: area-core-library, type-enhancement

Summary: The user proposes a new function truncateAsFixed() to truncate a double to a fixed number of decimal places without rounding, as toStringAsFixed() currently rounds the value. The user believes the rounding behavior of toStringAsFixed() is not sufficiently clear in the documentation.