CODEWITHSUNDEEP
f#
robi_one
robi_one

Reputation: 29

How to get the difference between two dates in F#?

Below is my attempt in creating a function that calculates the difference between two dates.

let test date =
    let today = DateTime.Now
    let fromdate = DateTime.Parse(date)
    let count = Convert.ToInt32(today - fromdate)
    date

The above code prompts the error

System.InvalidCastException: Unable to cast object of type 
'System.TimeSpan' to type 'System.IConvertible'.

Upvotes: 1

Views: 2878

Answers (2)

s952163
s952163

Reputation: 6324

The difference between two DateTimes will give you a TimeSpan object, on which you can further operate. This should be the last statement in your function, as it will be used as the return value. You can check the MS docs in the link for the various properties and methods. Strictly speaking, this is part of the BCL, so it's rather .NET than just F# (you would do the same in VB or C#). If you want to further refine your function you should examine DateTime.TryParse as well and handle the possibility of not receiving a valid date. 

open System

let test date =
    let today = DateTime.Now
    let fromdate = DateTime.Parse(date)
    (today - fromdate).Days

test "2017/12/31" // val it : int = -325

Upvotes: 2

Gebb
Gebb

Reputation: 6556

You don't need to convert the time span resulting from applying the "minus" operator to two dates. The screenshot below is my attempt at fixing your function and an example of value it returns.

Result of applying the fixed function

Upvotes: 0

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