The IData interface is a generic Interface for handling Data like NBT.
You can cast about all primitives (short, double, string, int, ...) as well as certain arrays to IData.
Remember that while they offer similar features, IData and their counterparts are NOT the same, which is why they will be referred to as DataTypes (e.g. DataBool).

It might be required for you to import the package if you encounter any issues (like casting an Array), so better be safe than sorry and add the import.
import crafttweaker.data.IData;

Binary Operators	+	-	*	/	%	&	|	^	in	==	<, >, <=, >=
Binary Operators DataBool	+ ✘	- ✘	* ✘	/ ✘	% ✘	& ✔	| ✔	^ ✔	in ✔	== ✔	<, >, <=, >= ✘
Binary Operators DataByte	+ ✔	- ✔	* ✔	/ ✔	% ✔	& ✔	| ✔	^ ✔	in ✔	== ✔	<, >, <=, >= ✔
Binary Operators DataByte[]	+ ✘	- ✘	* ✘	/ ✘	% ✘	& ✘	| ✘	^ ✘	in ✔	== ✔	<, >, <=, >= ✘
Binary Operators DataDouble	+ ✔	- ✔	* ✔	/ ✔	% ✔	& ✘	| ✘	^ ✘	in ✔	== ✔	<, >, <=, >= ✔
Binary Operators DataFloat	+ ✔	- ✔	* ✔	/ ✔	% ✔	& ✘	| ✘	^ ✘	in ✔	== ✔	<, >, <=, >= ✔
Binary Operators DataInt	+ ✔	- ✔	* ✔	/ ✔	% ✔	& ✔	| ✔	^ ✔	in ✔	== ✔	<, >, <=, >= ✔
Binary Operators DataInt[]	+ ✔	- ✘	* ✘	/ ✘	% ✘	& ✘	| ✘	^ ✘	in ✔	== ✔	<, >, <=, >= ✘
Binary Operators DataList	+ ✔	- ✘	* ✘	/ ✘	% ✘	& ✘	| ✘	^ ✘	in ✔	== ✔	<, >, <=, >= ✘
Binary Operators DataLong	+ ✔	- ✔	* ✔	/ ✔	% ✔	& ✔	| ✔	^ ✔	in ✔	== ✔	<, >, <=, >= ✔
Binary Operators DataMap	+ ✔	- ✔	* ✘	/ ✘	% ✘	& ✘	| ✘	^ ✘	in ✔	== ✔	<, >, <=, >= ✘
Binary Operators DataShort	+ ✔	- ✔	* ✔	/ ✔	% ✔	& ✔	| ✔	^ ✔	in ✔	== ✔	<, >, <=, >= ✔
Binary Operators DataString	+ ✔	- ✘	* ✘	/ ✘	% ✘	& ✘	| ✘	^ ✘	in ✔	== ✔	<, >, <=, >= ✔

Unary Oparators	- negate	! not
Unary Oparators DataBool	- negate ✘	! not ✔
Unary Oparators DataByte	- negate ✔	! not ✔
Unary Oparators DataByte[]	- negate ✘	! not ✘
Unary Oparators DataDouble	- negate ✔	! not ✘
Unary Oparators DataFloat	- negate ✔	! not ✘
Unary Oparators DataInt	- negate ✔	! not ✔
Unary Oparators DataInt[]	- negate ✘	! not ✘
Unary Oparators DataList	- negate ✘	! not ✘
Unary Oparators DataLong	- negate ✔	! not ✔
Unary Oparators DataMap	- negate ✘	! not ✘
Unary Oparators DataShort	- negate ✔	! not ✔
Unary Oparators DataString	- negate ✘	! not ✘

Index and Members	[i]	[i]=v	.member	.member=v	.length	.immutable	.update(v)
Index and Members DataBool	[i] ✘	[i]=v ✘	.member ✘	.member=v ✘	.length returns 0	.immutable ✔	.update(v) ✔
Index and Members DataByte	[i] ✘	[i]=v ✘	.member ✘	.member=v ✘	.length returns 0	.immutable ✔	.update(v) ✔
Index and Members DataByte[]	[i] ✔	[i]=v ✔	.member ✘	.member=v ✘	.length ✔	.immutable ✔	.update(v) ✔
Index and Members DataDouble	[i] ✘	[i]=v ✘	.member ✘	.member=v ✘	.length returns 0	.immutable ✔	.update(v) ✔
Index and Members DataFloat	[i] ✘	[i]=v ✘	.member ✘	.member=v ✘	.length returns 0	.immutable ✔	.update(v) ✔
Index and Members DataInt	[i] ✘	[i]=v ✘	.member ✘	.member=v ✘	.length returns 0	.immutable ✔	.update(v) ✔
Index and Members DataInt[]	[i] ✔	[i]=v ✔	.member ✘	.member=v ✘	.length ✔	.immutable ✔	.update(v) ✔
Index and Members DataList	[i] ✔	[i]=v ✔	.member ✘	.member=v ✘	.length ✔	.immutable ✔	.update(v) ✔
Index and Members DataLong	[i] ✘	[i]=v ✘	.member ✘	.member=v ✘	.length returns 0	.immutable ✔	.update(v) ✔
Index and Members DataMap	[i] ✘	[i]=v ✘	.member ✔	.member=v ✔	.length ✔	.immutable ✔	.update(v) ✔
Index and Members DataShort	[i] ✘	[i]=v ✘	.member ✘	.member=v ✘	.length returns 0	.immutable ✔	.update(v) ✔
Index and Members DataString	[i] ✔	[i]=v ✘	.member ✘	.member=v ✘	.length ✔	.immutable ✔	.update(v) ✔

You can cast IData to a specific type using data.asType() → data.asInt();
You can also use the IData Interface to convert types: ("1" as IData).asInt();

Casts from ↓ to →	bool	byte	byte[]	double	float	int	int[]	list	long	Map	short	string
Casts from ↓ to → DataBool	bool ≡	byte ✔	byte[] null	double ✔	float ✔	int ✔	int[] null	list null	long ✔	Map null	short ✔	string ✔
Casts from ↓ to → DataByte	bool ✔	byte ≡	byte[] null	double ✔	float ✔	int ✔	int[] null	list null	long ✔	Map null	short ✔	string ✔
Casts from ↓ to → DataByte[]	bool ✘	byte ✘	byte[] ≡	double ✘	float ✘	int ✘	int[] ✔	list ✔	long ✘	Map null	short ✘	string ✔
Casts from ↓ to → DataDouble	bool ✔	byte ✔	byte[] null	double ≡	float ✔	int ✔	int[] null	list null	long ✔	Map null	short ✔	string ✔
Casts from ↓ to → DataFloat	bool ✔	byte ✔	byte[] null	double ✔	float ≡	int ✔	int[] null	list null	long ✔	Map null	short ✔	string ✔
Casts from ↓ to → DataInt	bool ✔	byte ✔	byte[] null	double ✔	float ✔	int ≡	int[] null	list null	long ✔	Map null	short ✔	string ✔
Casts from ↓ to → DataInt[]	bool ✘	byte ✘	byte[] ✔	double ✘	float ✘	int ✘	int[] ≡	list ✔	long ✘	Map null	short ✘	string ✔
Casts from ↓ to → DataList	bool ✘	byte ✘	byte[] ✔	double ✘	float ✘	int ✘	int[] ✔	list ≡	long ✘	Map null	short ✘	string ✔
Casts from ↓ to → DataLong	bool ✔	byte ✔	byte[] null	double ✔	float ✔	int ✔	int[] null	list null	long ≡	Map null	short ✔	string ✔
Casts from ↓ to → DataMap	bool ✘	byte ✘	byte[] null	double ✘	float ✘	int ✘	int[] null	list null	long ✘	Map ≡	short ✘	string ✔
Casts from ↓ to → DataShort	bool ✔	byte ✔	byte[] null	double ✔	float ✔	int ✔	int[] null	list null	long ✔	Map null	short ≡	string ✔
Casts from ↓ to → DataString	bool ✘	byte ✔	byte[] null	double ✔	float ✔	int ✔	int[] null	list null	long ✔	Map null	short ✔	string ≡