Compare json values.

[Mark SiblyKeymaster]

Here’s some code to compare json values.

I initially tried to add something like this to the JsonValue class using the spaceship operator ‘<=>’, but this lead to some highly recursive problems because the spaceship operator redfines plain object compare etc, so stuff like ‘If Self=NullValue’ would cause the stack to explode!

This highlights the difficulty involved in overloading comparison operators for reference types (ie: classes) and it’s something I’d recommend avoiding altogether. It’s still quite all right to provide comparison operators for value types though (ie: structs).

It also underlines the need for more flexible comparison functionality in things like Map, to allow you to create eg: a  Map<JsonValue,Blah> using code like this without having to define <=> for JsonValue.

Monkey

#Import "<std>" Using std.. Function CompareJson:Int( x:JsonObject,y:JsonValue ) If y=JsonValue.NullValue Return 1 Local r:=Cast<JsonObject>( y ) If Not r Return 1 Local xit:=x.All(),rit:=r.All() While Not xit.AtEnd And Not rit.AtEnd Local cmp:=xit.Current.Key<=>rit.Current.Key If cmp Return cmp cmp=CompareJson( xit.Current.Value,rit.Current.Value ) If cmp Return cmp xit.Bump() rit.Bump() Wend Return x.Count()<=>r.Count() End Function CompareJson:Int( x:JsonArray,y:JsonValue ) If y=JsonValue.NullValue Or y.IsBool Or y.IsNumber Or y.IsString Return 1 Local r:=Cast<JsonArray>( y ) If Not r Return -1 For Local i:=0 Until Min( x.Length,r.Length ) Local cmp:=CompareJson( x[i],r[i] ) If cmp Return cmp Next Return x.Length<=>r.Length End Function CompareJson:Int( x:JsonString,y:JsonValue ) If y=JsonValue.NullValue Or y.IsBool Or y.IsNumber Return 1 Local r:=Cast<JsonString>( y ) Return r ? x.Data<=>r.Data Else -1 End Function CompareJson:Int( x:JsonNumber,y:JsonValue ) If y=JsonValue.NullValue Or y.IsBool Return 1 Local r:=Cast<JsonNumber>( y ) Return r ? x.Data<=>r.Data Else -1 End Function CompareJson:Int( x:JsonBool,y:JsonValue ) If y=JsonValue.NullValue Return 1 Local r:=Cast<JsonBool>( y ) Return r ? x.Data<=>r.Data Else -1 End Function CompareJson:Int( x:JsonValue,y:JsonValue ) If x=JsonValue.NullValue Return y=JsonValue.NullValue ? 0 Else -1 Local jbool:=Cast<JsonBool>( x ) If jbool Return CompareJson( jbool,y ) Local jnumber:=Cast<JsonNumber>( x ) If jnumber Return CompareJson( jnumber,y ) Local jstring:=Cast<JsonString>( x ) If jstring Return CompareJson( jstring,y ) local jarray:=Cast<JsonArray>( x ) If jarray Return CompareJson( jarray,y ) Local jobj:=Cast<JsonObject>( x ) If jobj Return CompareJson( jobj,y ) RuntimeError( "TODO" ) Return 0 End Function RndJson:JsonValue( range:Int=6 ) Select Int( Rnd( range ) ) Case 0 Return JsonValue.NullValue Case 1 Return Rnd()>.5 ? JsonBool.TrueValue Else JsonBool.FalseValue Case 2 Return New JsonNumber( Rnd(10000) ) Case 3 Return New JsonString( Rnd(10000) ) Case 4 Local data:=New Stack<JsonValue>( Rnd( 10,20 ) ) For Local i:=0 Until data.Length data[i]=RndJson( 4 ) Next Return New JsonArray( data ) Case 5 Local data:=New StringMap<JsonValue> For Local i:=0 Until Rnd( 10,20 ) data[ Rnd(100) ]=RndJson( 4 ) Next Return New JsonObject( data ) End Return Null End Function Main() Print "Start..." For Local i:=1 To 100000 Local x:=RndJson() Local y:=RndJson() Local cmp1:=CompareJson( x,y ) Local cmp2:=CompareJson( y,x ) If cmp1<0 Assert( cmp2>=0 ) If cmp1=0 Assert( cmp2 =0 ) If cmp1>0 Assert( cmp2<=0 ) End Print "Success!" End

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#Import "<std>"   Using std..   Function CompareJson:Int( x:JsonObject,y:JsonValue ) If y=JsonValue.NullValue Return 1 Local r:=Cast<JsonObject>( y ) If Not r Return 1 Local xit:=x.All(),rit:=r.All() While Not xit.AtEnd And Not rit.AtEnd Local cmp:=xit.Current.Key<=>rit.Current.Key If cmp Return cmp cmp=CompareJson( xit.Current.Value,rit.Current.Value ) If cmp Return cmp xit.Bump() rit.Bump() Wend Return x.Count()<=>r.Count() End   Function CompareJson:Int( x:JsonArray,y:JsonValue ) If y=JsonValue.NullValue Or y.IsBool Or y.IsNumber Or y.IsString Return 1 Local r:=Cast<JsonArray>( y ) If Not r Return -1 For Local i:=0 Until Min( x.Length,r.Length ) Local cmp:=CompareJson( x[i],r[i] ) If cmp Return cmp Next Return x.Length<=>r.Length End   Function CompareJson:Int( x:JsonString,y:JsonValue ) If y=JsonValue.NullValue Or y.IsBool Or y.IsNumber Return 1 Local r:=Cast<JsonString>( y ) Return r ? x.Data<=>r.Data Else -1 End   Function CompareJson:Int( x:JsonNumber,y:JsonValue ) If y=JsonValue.NullValue Or y.IsBool Return 1 Local r:=Cast<JsonNumber>( y ) Return r ? x.Data<=>r.Data Else -1 End   Function CompareJson:Int( x:JsonBool,y:JsonValue ) If y=JsonValue.NullValue Return 1 Local r:=Cast<JsonBool>( y ) Return r ? x.Data<=>r.Data Else -1 End   Function CompareJson:Int( x:JsonValue,y:JsonValue ) If x=JsonValue.NullValue Return y=JsonValue.NullValue ? 0 Else -1 Local jbool:=Cast<JsonBool>( x ) If jbool Return CompareJson( jbool,y ) Local jnumber:=Cast<JsonNumber>( x ) If jnumber Return CompareJson( jnumber,y ) Local jstring:=Cast<JsonString>( x ) If jstring Return CompareJson( jstring,y ) local jarray:=Cast<JsonArray>( x ) If jarray Return CompareJson( jarray,y ) Local jobj:=Cast<JsonObject>( x ) If jobj Return CompareJson( jobj,y ) RuntimeError( "TODO" ) Return 0 End   Function RndJson:JsonValue( range:Int=6 ) Select Int( Rnd( range ) ) Case 0 Return JsonValue.NullValue Case 1 Return Rnd()>.5 ? JsonBool.TrueValue Else JsonBool.FalseValue Case 2 Return New JsonNumber( Rnd(10000) ) Case 3 Return New JsonString( Rnd(10000) ) Case 4 Local data:=New Stack<JsonValue>( Rnd( 10,20 ) ) For Local i:=0 Until data.Length data[i]=RndJson( 4 ) Next Return New JsonArray( data ) Case 5 Local data:=New StringMap<JsonValue> For Local i:=0 Until Rnd( 10,20 ) data[ Rnd(100) ]=RndJson( 4 ) Next Return New JsonObject( data ) End Return Null End   Function Main() Print "Start..." For Local i:=1 To 100000 Local x:=RndJson() Local y:=RndJson() Local cmp1:=CompareJson( x,y ) Local cmp2:=CompareJson( y,x ) If cmp1<0 Assert( cmp2>=0 ) If cmp1=0 Assert( cmp2 =0 ) If cmp1>0 Assert( cmp2<=0 ) End Print "Success!" End

[EthernautParticipant]

So, let me see if I understand correctly… if the json values are identical it returns zero?
(I always forget what the “<=>” operator does…)

[Mark SiblyKeymaster]

Yes, x<=>y produces…

an int value=0 if x=y,

an int value<0 if x<y or

an int value>0 if x>y.

[nerobotParticipant]

There may be a virtual method CompareTo:Int( value:JsonValue ) of JsonValue.

By default it will return -1.

And any sub-classes will override it.

Technically it will be the same as your functions above.

The difference is a way of call: json1.CompareTo( json2 ) in this case.

If we aware of nullability of json1, then we can use ?. operator.

Also in your code you check y=NullValue and return 1 if true, but x can be null itself and then we should get zero in result.

Sorry, I did’n understand about stack exploding reason.

If we use just functions like ones above – do we avoid stack exploding when using if Self.IsNull?

(JsonValue has a property IsNull.)

[nerobotParticipant]

If we declare new sub-class JsonNull extends JsonValue and replace current NullValue with them – will it helps us to check if x is null-value w/o any stack-ish problems?

[Mark SiblyKeymaster]

Yes, adding a JsonNull class is probably a better way to do the null value thing, and would prevent at least that particular stack explosion. Are there any others?

I’m still a bit weird about comparing references in fancy ways, just been bitten by it so many times in c++ perhaps. I probably just need to go ahead and do it?

Also in your code you check y=NullValue and return 1 if true, but x can be null itself and then we should get zero in result.

Where in the code? There is a check in the ‘root’ CompareJon for when x and y are both null and it returns 0 there. This is the only place where x can be null, and in all other cases, x is always > null.

The little RndJson test seems to work OK too.

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