How to multiply duration by integer

Question

To test concurrent goroutines  I added a line to a function to make it take a random time to return  up to one second   time Sleep rand Int31n 1000    time Millisecond    However when I compiled  I got this error       crawler go 49  invalid operation  rand Int31n 1000    time Millisecond  mismatched types int32 and time Duration    Any ideas  How can I multiply a duration

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My turn  https   play golang org p RifHKsX7Puh package main  import        quot fmt quot       quot time quot     func main         var n int   77     v    time Duration  1 15   float64 n      time Second      fmt Printf  quot  v  T quot   v  v     It helps to remember the simple fact  that underlyingly the time Duration is a mere int64  which holds nanoseconds value  This way  conversion to from time Duration becomes a formality  Just remember   int64 always nanosecs

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In Go  you can multiply variables of same type  so you need to have both parts of the expression the same type  The simplest thing you can do is casting an integer to duration before multiplying  but that would violate unit semantics  What would be multiplication of duration by duration in term of units  I d rather convert time Millisecond to an int64  and then multiply it by the number of milliseconds  then cast to time Duration  time Duration int64 time Millisecond    int64 rand Int31n 1000     This way any part of the expression can be said to have a meaningful value according to its type  int64 time Millisecond  part is just a dimensionless value - the number of smallest units of time in the original value  If walk a slightly simpler path  time Duration rand Int31n 1000     time Millisecond  The left part of multiplication is nonsense - a value of type  quot time Duration quot   holding something irrelevant to its type  numberOfMilliseconds    100    just can t come up with a name for following  someLHS    time Duration numberOfMilliseconds  fmt Println someLHS  fmt Println someLHS time Millisecond   And it s not just semantics  there is actual functionality associated with types  This code prints  100ns 100ms  Interestingly  the code sample here uses the simplest code  with the same misleading semantics of Duration conversion  https   golang org pkg time  Duration  seconds    10 fmt Print time Duration seconds  time Second     prints 10s

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For multiplication of variable to time Second using following code      oneHr  3600     addOneHrDuration   time Duration oneHr      addOneHrCurrTime    time Now   Add addOneHrDuration time Second

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int32 and time Duration are different types  You need to convert the int32 to a time Duration  such as time Sleep time Duration rand Int31n 1000     time Millisecond

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It s nice that Go has a Duration type -- having explicitly defined units can prevent real-world problems   And because of Go s strict type rules  you can t multiply a Duration by an integer -- you must use a cast in order to multiply common types      MultiplyDuration Hide semantically invalid duration math behind a function    func MultiplyDuration factor int64  d time Duration  time Duration       return time Duration factor    d           method 1 -- multiply in  Duration      return time Duration factor   int64 d      method 2 -- multiply in  int64      The official documentation demonstrates using method  1      To convert an integer number of units to a Duration  multiply    seconds    10 fmt Print time Duration seconds  time Second     prints 10s   But  of course  multiplying a duration by a duration should not produce a duration -- that s nonsensical on the face of it   Case in point  5 milliseconds times 5 milliseconds produces 6h56m40s   Attempting to square 5 seconds results in an overflow  and won t even compile if done with constants    By the way  the int64 representation of Duration in nanoseconds  limits the largest representable duration to approximately 290 years   and this indicates that Duration  like int64  is treated as a signed value   1 lt  lt  64-1    1e9 60 60 24 365 25     292  and that s exactly how it is implemented      A Duration represents the elapsed time between two instants    as an int64 nanosecond count  The representation limits the    largest representable duration to approximately 290 years  type Duration int64   So  because we know that the underlying representation of Duration is an int64  performing the cast between int64 and Duration is a sensible NO-OP -- required only to satisfy language rules about mixing types  and it has no effect on the subsequent multiplication operation   If you don t like the the casting for reasons of purity  bury it in a function call as I have shown above

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You have to cast it to a correct format Playground   yourTime    rand Int31n 1000  time Sleep time Duration yourTime    time Millisecond      If you will check documentation for sleep  you see that it requires func Sleep d Duration  duration as a parameter  Your rand Int31n returns int32    The line from the example works  time Sleep 100   time Millisecond   because the compiler is smart enough to understand that here your constant 100 means a duration  But if you pass a variable  you should cast it

[go] How to multiply duration by integer?

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