unit phTriState;
interface
type
TriState_=(tsFalse=0, tsTrue=1,tsNull=2);
TriState=record
private
value:TriState_;
public
class operator Implicit(v:TriState):Boolean;
class operator Implicit(v:TriState_):TriState;
class operator Implicit(v:boolean):TriState;
class operator Equal(my:Tristate; their:Boolean):Boolean;
class operator Equal(my:Tristate; their:TriState_):Boolean;
class operator LogicalAnd(my: TriState; b: boolean): TriState;
class operator LogicalAnd(my: TriState; b: TriState): TriState;
class operator Explicit(v:TriState):Boolean;
end;
implementation
{ TriState }
class operator TriState.Equal(my: Tristate;
their: TriState_): Boolean;
begin
Result:=my.value=their;
end;
class operator TriState.Explicit(v: TriState): Boolean;
begin
result:=v
end;
class operator TriState.Equal(my: Tristate;
their: Boolean): Boolean;
begin
result:= (Ord(my.value)=Ord(their))
end;
class operator TriState.Implicit(v: TriState): Boolean;
begin
result:= (v.value<>tsNull) and (Boolean(v.value));
end;
class operator TriState.Implicit(v: boolean): TriState;
begin
result.value:=TRistate_(Ord(v));
end;
class operator TriState.LogicalAnd(my,
b: TriState): TriState;
begin
if (my.value=tsNull) or (b.value=tsNull) then Result.value:=tsNull
else Result.value:=Tristate_(Boolean(ord(my.value)) and Boolean(Ord(b.value)));
end;
class operator TriState.LogicalAnd(my: TriState;
b: boolean): TriState;
var nv:Tristate;
begin
nv:=b;
result:= my and nv;
end;
class operator TriState.Implicit(v: TriState_): TriState;
begin
Result.value:=v;
end;
end.
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