Duration class doesn't contain weeks, months and years

[DartBot]

This issue was originally filed by svangrieke...@google.com

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What steps will reproduce the problem?
The Duration class doesn't contain weeks, months and years.

What is the expected output? What do you see instead?
I would like to have a duration in months, weeks and years.

What version of the product are you using? On what operating system?
Build 22223 on Mac OSx

Please provide any additional information below.
I want to iterate over a list of months given two DateTime instances. The counter should be set with the number of months between these two dates.

[DartBot]

This comment was originally written by svangrieke...@google.com

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Area: libraries dart:core

[DartBot]

This comment was originally written by @seaneagan

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dupe of issue #1426. this could be part of the library referenced by issue #5627.

[madsager]

Added Area-Library, Triaged labels.

[lrhn]

The problem with months and years as duration is that they don't always have the same length, or even a reasonable default length. Days have a reasonable 24 hour default length, even if daylight saving makes 23 and 25 occur, but months range between 28 and 31 days, and years between 365 and 366 days,

Duration is really a count of milliseconds (or less), so it's not possible to say how much that is in "months", and even if we had something representing the abstract concept of a "month duration", it's not obvious what would happen if you added that to 2010-01-30 - would you get 2010-02-28, 2010-03-01 or 2010-03-02? All three can be argued.

Weeks (aka. 7 days of 24 hours) should be doable, though.

[floitschG]

Weeks would be possible, but weeks really aren't used that much. Our time-system is based on Year-month-day, hour-minutes-seconds-subseconds.

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Added WontFix label.