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    Class Unit

    Unit models a unit of measurement. Units are represented as:

    • ids: each unit has one or more unique identifiers for the unit within the VM. Units are typically defined in the unit database "etc/sys/units.txt" or can be via by the define method. Every id assigned to a unit must be unique within the VM.
    • name: the first identifier in the ids list is called the name and should be a descriptive summary of the unit using words separated by underbar such as "miles_per_hour".
    • symbol: the last identifier in the ids list should be the abbreviated symbol; for example "kilogram" has the symbol "kg". In units with only one id, the symbol is the same as the name. Units with exponents should use Unicode superscript chars, not ASCII digits.
    • dimension: defines the ratio of the seven SI base units: m, kg, sec, A, K, mol, and cd
    • scale/factor: defines the normalization equations for unit conversion

    A unit identifier is limited to the following characters:

    • any Unicode char over 128
    • ASCII letters a - z and A - Z
    • underbar _
    • division sign /
    • percent sign %
    • dollar sign $

    Units with equal dimensions are considered to measure the same physical quantity. This is not always true, but good enough for practice. Conversions with the convertTo method are expressed with the following equations:

    unit       = dimension * scale + offset
    toNormal   = scalar * scale + offset
    fromNormal = (scalar - offset) / scale
    toUnit     = fromUnit.fromNormal( toUnit.toNormal(sclar) )

    As a simple, pragmatic solution for modeling Units, there are some units which don't fit this model including logarithm and angular units. Units which don't cleanly fit this model should be represented as dimensionless (all ratios set to zero).

    Fantom's model for units of measurement and the unit database are derived from the OASIS oBIX specification.

    Hierarchy (View Summary)

    Index

    Constructors

    constructor

    Properties

    type$

    Methods

    A cd compare convertTo definition dim div equals hash ids isImmutable K kg m mol mult name offset scale sec symbol toImmutable toStr trap typeof with define echo fromStr list make quantities quantity

    Constructors

    Properties

    type$: Type

    Methods

    • Ampere (electric current) component of the unit dimension.

      Returns number

    • Candela (luminous intensity) component of the unit dimension.

      Returns number

    • Return a negative integer, zero, or a positive integer if this object is less than, equal to, or greater than the specified object:

      this < that   =>  <0
      this == that  =>  0
      this > that   =>  >0

      This method may also be accessed via the < <= <=> >= and > shortcut operators. If not overridden the default implementation compares the toStr representations. Also see docLang.

      Examples:

      3.compare(8)  =>  -1
      8.compare(3)  =>  1
      8.compare(8)  =>  0
      3 <=> 8       =>  -1  // shortcut for 3.compare(8)

      Parameters

      Returns number

    • Convert a scalar value from this unit to the given unit. If the units do not have the same dimension then throw Err. For example, to convert 3km to meters:

      m  := Unit("meter")
      km := Unit("kilometer")
      km.convertTo(3f, m)  =>  3000f

      Parameters

      • scalar: number
      • unit: Unit

      Returns number

    • Return string format as specified by define.

      Returns string

    • Return the string format of the dimension portion of definition

      Returns string

    • Match quotient of this divided by b against current database definitions. If an unambiguous match cannot be made then throw Err.

      Parameters

      Returns Unit

    • Two units are equal if they have reference equality because all units are interned during definition.

      Parameters

      Returns boolean

    • Return toStr.hash.

      Returns number

    • Return the list of programmatic identifiers for this unit. The first item is always name and the last is always symbol.

      Returns List<string>

    • Return if this Obj is immutable and safe to share between threads:

      • an instance of a const class
      • the result of toImmutable on List, Map, or Buf
      • a Func object may or may not be immutable - see sys::Func.
      • other instances are assumed mutable and return false

      Returns boolean

    • Kelvin (thermodynamic temperature) component of the unit dimension.

      Returns number

    • Kilogram (mass) component of the unit dimension.

      Returns number

    • Meter (length) component of the unit dimension.

      Returns number

    • Mole (amount of substance) component of the unit dimension.

      Returns number

    • Match the product of this and b against current database definitions. If an unambiguous match cannot be made then throw Err.

      Parameters

      Returns Unit

    • Return the primary name identifier of this unit. This is always the first item in ids.

      Returns string

    • Return the offset factor used to convert this unit "from normal". See class header for normalization and conversion equations. Offset is used most commonly with temperature units. The offset for normalized unit is always zero.

      Returns number

    • Return the scale factor used to convert this unit "from normal". For example the scale factor for kilometer is 1000 because it is defined as a 1000 meters where meter is the normalized unit for length. See class header for normalization and conversion equations. The scale factor for the normalized unit is always one.

      Returns number

    • Second (time) component of the unit dimension.

      Returns number

    • Return the abbreviated symbol for this unit. This is always the last item in ids.

      Returns string

    • Get an immutable representation of this instance or throw NotImmutableErr if this object cannot be represented as an immutable:

      • if type is const, return this
      • if already an immutable List, Map, Buf, or Func return this
      • if a List, then attempt to perform a deep clone by calling toImmutable on all items
      • if a Map, then attempt to perform a deep clone by calling toImmutable on all values (keys are already immutable)
      • some Funcs can be made immutable - see sys::Func
      • if a Buf create immutable copy, see sys::Buf
      • any other object throws NotImmutableErr

      Returns Readonly<this>

    • Return symbol.

      Returns string

    • Trap a dynamic call for handling. Dynamic calls are invoked with the -> shortcut operator:

      a->x        a.trap("x", null)
      a->x()      a.trap("x", null)
      a->x = b    a.trap("x", [b])
      a->x(b)     a.trap("x", [b])
      a->x(b, c)  a.trap("x", [b, c])

      The default implementation provided by Obj attempts to use reflection. If name maps to a method, it is invoked with the specified arguments. If name maps to a field and args.size is zero, get the field. If name maps to a field and args.size is one, set the field and return args[0]. Otherwise throw UnknownSlotErr.

      Parameters

      Returns JsObj

    • Get the Type instance which represents this object's class. Also seeType.of or Pod.of.

      Returns Type

    • This method called whenever an it-block is applied to an object. The default implementation calls the function with this, and then returns this.

      Parameters

      • f: (arg0: this) => void

      Returns this

    • Define a new Unit definition in the VM's unit database using the following string format:

      unit   := <ids> [";" <dim> [";" <scale> [";" <offset>]]]
      names  := <ids> ("," <id>)*
      id     := <idChar>*
      idChar := 'a'-'z' | 'A'-'Z' | '_' | '%' | '/' | any char > 128
      dim    := <ratio> ["*" <ratio>]*   // no whitespace allowed
      ratio  := <base> <exp>
      base   := "kg" | "m" | "sec" | "K" | "A" | "mol" | "cd"
      exp    := <int>
      scale  := <float>
      offset := <float>

      If the format is incorrect or any identifiers are already defined then throw an exception.

      Parameters

      • s: string

      Returns Unit

    • Write x.toStr to standard output followed by newline. If x is null then print "null". If no argument is provided then print an empty line.

      Parameters

      Returns void

    • Find a unit by one of its identifiers if it has been defined in this VM. If the unit isn't defined yet and checked is false then return null, otherwise throw Err. Any units declared in "etc/sys/units.txt" are implicitly defined.

      Parameters

      • s: string
      • Optionalchecked: boolean
      • ...args: unknown[]

      Returns Unit

    • List all the units currently defined in the VM. Any units declared in "etc/sys/units.txt" are implicitly defined.

      Returns List<Unit>

    • Parameters

      • ...args: unknown[]

      Returns Unit

    • List the quantity names used to organize the unit database in "etc/sys/units.txt". Quantities are merely a convenient mechanism to organize the unit database - there is no guarantee that they include all current VM definitions.

      Returns List<string>

    • Get the units organized under a specific quantity name in the unit database "etc/sys/units.txt". Quantities are merely a convenient mechanism to organize the unit database

      • there is no guarantee that they include all current VM definitions.

      Parameters

      • quantity: string

      Returns List<Unit>

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