When querying a number, you can check whether the number can be obtained as target type:
Checking | Obtaining
-------------|--------------
`IsNumber()` | N/A
`IsInt()` | `GetInt()`
`IsUint()` | `GetUint()`
`IsInt64()` | `GetInt64()`
`IsUint64()` | `GetUint()`
`IsDouble()` | `GetDouble()`
Checking | Obtaining
------------------|---------------------
`bool IsNumber()` | N/A
`bool IsInt()` | `int GetInt()`
`bool IsUint()` | `unsigned GetUint()`
`bool IsInt64()` | `uint64_t GetInt64()`
`bool IsUint64()` | `int64_t GetUint()`
`bool IsDouble()` | `double GetDouble()`
Note that, an integer value may be obtained in various ways without conversion. For example, A value `x` containing `123` will make `x.IsInt() == x.IsUint() == x.Int64() == x.Uint64() == ture`. But a value `y` containing `-3000000000` will only makes `x.int64() == true`.
