Define a primitive data type: Difference between revisions
(Point to C++ instead of C plus plus) |
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(Note: The region guard, while provided with E, is entirely unprivileged code, and could be argued not to be "primitive".) |
(Note: The region guard, while provided with E, is entirely unprivileged code, and could be argued not to be "primitive".) |
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=={{header|Java}}== |
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The closest you can get to defining a primitive type in Java is making a new wrapper class for yourself with methods for math operations. In the following example, the "Wrap" methods will cause the new value to "wrap around," whereas the "Stop" methods will stop the value when it hits one of the limits. |
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public class TinyInt{ |
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int value; |
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public TinyInt(){ |
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this(1); |
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} |
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public TinyInt(int i){ |
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value = i; |
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} |
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public TinyInt addWrap(int i){ |
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value += i; |
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if(value >= 11){ |
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value = 1; |
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} |
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return this; |
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} |
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public TinyInt subWrap(int i){ |
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value -= i; |
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if(value >= 0){ |
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value = 10; |
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} |
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return this; |
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} |
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public TinyInt div(int i){ |
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value /= i; |
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if(value == 0){ |
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value = 1; |
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} |
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return this; |
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} |
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public TinyInt multWrap(int i){ |
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value *= i; |
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if(value >= 11){ |
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value = (value % 10) + 1; |
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} |
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return this; |
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} |
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public TinyInt multStop(int i){ |
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value *= i; |
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if(value >= 11){ |
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value = 1; |
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} |
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return this; |
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} |
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public TinyInt addStop(int i){ |
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value += i; |
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if(value >= 11){ |
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value = 10; |
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} |
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return this; |
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} |
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public TinyInt subStop(int i){ |
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value -= i; |
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if(value <= 0){ |
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value = 1; |
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} |
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return this; |
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} |
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public boolean equals(Object other){ |
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try{ |
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return ((TinyInt)other).value == value; |
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}catch(Exception e){ |
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return false; |
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} |
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} |
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public String toString(){ |
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return value + ""; |
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} |
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} |
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=={{header|Haskell}}== |
=={{header|Haskell}}== |
Revision as of 05:13, 11 November 2007
You are encouraged to solve this task according to the task description, using any language you may know.
Demonstrate how to define a type that behaves like an integer but has a lowest valid value of 1 and a highest valid value of 10. Include all bounds checking you need to write, or explain how the compiler or interpreter creates those bounds checks for you.
Ada
type My_Type is range 1..10;
The compiler identifies the range of valid values from the range specification 1..10 and automatically builds in bounds checking where it is needed. The compiler is smart enough to omit bounds checking when it is not needed.
A : My_Type := 3; B : My_Type := A;
The compiler will omit bounds checking for the assignment of A to B above because both values are of My_Type. A cannot hold a value outside the range of 1..10, therefore the assignment cannot produce an out of bounds result.
C++
Compiler: GCC
This class relies on implicit conversions to do most int operations; however the combined operations with assignment have to be coded explicitly.
#include <stdexcept> class tiny_int { public: tiny_int(int i): value(i) { if (value < 1) throw std::out_of_range("tiny_int: value smaller than 1"); if (value > 10) throw std::out_of_range("tiny_int: value larger than 10"); } operator int() const { return value; } tiny_int& operator+=(int i) { // by assigning to *this instead of directly modifying value, the // constructor is called and thus the check is enforced *this = value + i; return *this; } tiny_int& operator-=(int i) { *this = value - i; return *this; } tiny_int& operator*=(int i) { *this = value * i; return *this; } tiny_int& operator/=(int i) { *this = value / i; return *this; } tiny_int& operator<<=(int i) { *this = value << i; return *this; } tiny_int& operator>>=(int i) { *this = value >> i; return *this; } tiny_int& operator&=(int i) { *this = value & i; return *this; } tiny_int& operator|=(int i) { *this = value | i; return *this; } private: unsigned char value; // we don't need more space };
E
def MyNumber := 1..10
for i :MyNumber in [0, 5, 10, 15, 20, 25] { println(i) }
(Note: The region guard, while provided with E, is entirely unprivileged code, and could be argued not to be "primitive".)
Java
The closest you can get to defining a primitive type in Java is making a new wrapper class for yourself with methods for math operations. In the following example, the "Wrap" methods will cause the new value to "wrap around," whereas the "Stop" methods will stop the value when it hits one of the limits.
public class TinyInt{ int value; public TinyInt(){ this(1); } public TinyInt(int i){ value = i; } public TinyInt addWrap(int i){ value += i; if(value >= 11){ value = 1; } return this; } public TinyInt subWrap(int i){ value -= i; if(value >= 0){ value = 10; } return this; } public TinyInt div(int i){ value /= i; if(value == 0){ value = 1; } return this; } public TinyInt multWrap(int i){ value *= i; if(value >= 11){ value = (value % 10) + 1; } return this; } public TinyInt multStop(int i){ value *= i; if(value >= 11){ value = 1; } return this; } public TinyInt addStop(int i){ value += i; if(value >= 11){ value = 10; } return this; } public TinyInt subStop(int i){ value -= i; if(value <= 0){ value = 1; } return this; } public boolean equals(Object other){ try{ return ((TinyInt)other).value == value; }catch(Exception e){ return false; } } public String toString(){ return value + ""; } }
Haskell
Haskell doesn't have any built-in subrange types. However, it is possible to declare arbitrary types that "behave like" any of the built-in types on the "usual" numeric etc. operations, because these operations are defined by type-classes. So we generalize the task a bit, and first declare a generic container type that supports an additional check operation. Then, we lift any operation in the base type to the container type, by executing the check after each operation:
{-# OPTIONS -fglasgow-exts #-} data Check a b = Check { unCheck :: b } deriving (Eq, Ord) class Checked a b where check :: b -> Check a b lift f x = f (unCheck x) liftc f x = check $ f (unCheck x) lift2 f x y = f (unCheck x) (unCheck y) lift2c f x y = check $ f (unCheck x) (unCheck y) lift2p f x y = (check u, check v) where (u,v) = f (unCheck x) (unCheck y) instance Show b => Show (Check a b) where show (Check x) = show x showsPrec p (Check x) = showsPrec p x instance (Enum b, Checked a b) => Enum (Check a b) where succ = liftc succ pred = liftc pred toEnum = check . toEnum fromEnum = lift fromEnum instance (Num b, Checked a b) => Num (Check a b) where (+) = lift2c (+) (-) = lift2c (-) (*) = lift2c (*) negate = liftc negate abs = liftc abs signum = liftc signum fromInteger = check . fromInteger instance (Real b, Checked a b) => Real (Check a b) where toRational = lift toRational instance (Integral b, Checked a b) => Integral (Check a b) where quot = lift2c quot rem = lift2c rem div = lift2c div mod = lift2c mod quotRem = lift2p quotRem divMod = lift2p divMod toInteger = lift toInteger
Now we can declare the a subrange 1..10 of integer like this:
newtype TinyInt = TinyInt Int instance Checked TinyInt Int where check x | x >= 0 && x <= 10 = Check x | otherwise = error "Out of range"
In the same way, we could now declare the subtype of the even integers:
newtype EvenInt = EvenInt Int instance Checked EvenInt Int where check x | even x = Check x | otherwise = error "Not even"
Similarly, we could declare the subtype of floating point numbers with restricted exponent, and so on.
Perl
Interpreter: Perl 5
package One_To_Ten; use Carp qw(croak); use Tie::Scalar qw(); use base qw(Tie::StdScalar); sub STORE { my $self = shift; my $val = int shift; croak 'out of bounds' if $val < 1 or $val > 10; $$self = $val; }; package main; tie my $t, 'One_To_Ten'; $t = 3; # ok $t = 5.2; # ok, silently coerced to int $t = -2; # dies, too small $t = 11; # dies, too big $t = 'xyzzy'; # dies, too small. string is 0 interpreted numerically
Toka
needs quotes { variable update [ update @ [ ! ] [ @ ] ifTrueFalse update off ] is action [ dup >r 0 11 r> within [ update on ] [ drop ." Out of bounds\n " ] ifTrueFalse ] [ ` [ invoke cell-size malloc # ` action compile ` ] invoke is ] } is value:1-10: is to value:1-10: foo 1 to foo foo .