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Create a domain element
This functionality does not run in MATLAB.
new(T, object1, object2, …)
Within a method of the domain type T, new(T, object1, object2, ...) creates a new element of the domain T with the internal representation object1, object2, ....
new is a low-level function for creating elements of library domains.
The internal representation of a domain element comprises a reference to the corresponding domain and an arbitrary number of MuPAD^{®} objects, the internal operands of the domain element.
new(T, object1, object2, ...) creates a new element of the domain T, whose internal representation is the sequence of operands object1, object2, ..., and returns this element.
new(T) creates a new element of the domain T, whose internal representation is an empty sequence of operands.
Note: new is intended only for programmers implementing their own domains in MuPAD. You should never use new directly to generate elements of a predefined domain T; use the corresponding constructor T(...) instead, for the following reasons. The internal representation of the predefined MuPAD domains may be subject to changes more often than the interface provided by the constructor. Moreover, in contrast to new, the constructors usually perform argument checking. Thus using new directly may lead to invalid internal representations of MuPAD objects. |
New domains can be created via newDomain.
You can access the operands of the internal representation of a domain element via extop, which, in contrast to op, cannot be overloaded for the domain. The function op is sometimes overloaded for a domain in order to hide the internal, technical representation of an object and to provide a more user friendly and intuitive interface.
Similarly, the function extnops returns the number of operands of a domain element in the internal representation, and extsubsop modifies an operand in the internal representation. These functions, in contrast to the related functions nops and subsop, cannot be overloaded for a domain.
You can write a constructor for your own domain T by providing a "new" method. This method is invoked whenever the user calls T(arg1, arg2, ...). This is recommended since it provides a more elegant and intuitive user interface than new. The "new" method usually performs some argument checking and converts the arguments arg1, arg2, ... into the internal representation of the domain, using new (see Example 1).
We create a new domain Time for representing clock times. The internal representation of an object of this domain has two operands: the hour and the minutes. Then we create a new domain element for the time 12:45:
Time := newDomain("Time"): a := new(Time, 12, 45)
The domain type of a is Time, the number of operands is 2, and the operands are 12 and 45:
domtype(a), extnops(a)
extop(a)
We now implement a "new" method for our new domain Time, permitting several input formats. It expects either two integers, the hour and the minutes, or only one integer that represents the minutes, or a rational number or a floating-point number, implying that the integral part is the hour and the fractional part represents a fraction of an hour corresponding to the minutes, or no arguments, representing midnight. Additionally, the procedure checks that the arguments are of the correct type:
Time::new := proc(HR = 0, MN = 0) local m; begin if args(0) = 2 and domtype(HR) = DOM_INT and domtype(MN) = DOM_INT then m := HR*60 + MN elif args(0) = 1 and domtype(HR) = DOM_INT then m := HR elif args(0) = 1 and domtype(HR) = DOM_RAT then m := trunc(float(HR))*60 + frac(float(HR))*60 elif args(0) = 1 and domtype(HR) = DOM_FLOAT then m := trunc(HR)*60 + frac(HR)*60 elif args(0) = 0 then m := 0 else error("wrong number or type of arguments") end_if; new(Time, trunc(m/60), trunc(m) mod 60) end_proc:
Now we can use this method to create new objects of the domain Time, either by calling Time::new directly, or, preferably, by using the equivalent but shorter call Time(...):
Time::new(12, 45), Time(12, 45), Time(12 + 3/4)
Time(), Time(8.25), Time(1/2)
In order to have a nicer output for objects of the domain Time, we also define a "print" method (see the help page for print):
Time::print := proc(TM) begin expr2text(extop(TM, 1)) . ":" . stringlib::format(expr2text(extop(TM, 2)), 2, Right, "0") end_proc:
Time::new(12, 45), Time(12, 45), Time(12 + 3/4)
Time(), Time(8.25), Time(1/2)