Taichi is a statically typed programming language: The type of a variable in the Taichi scope is determined at compile time; once a variable is declared, you cannot assign to it a value of a different type.
Let's see a quick example:
x = 1 # x is the integer 1
x = 3.14 # x is an integer, so the value 3.14 is cast to 3 and x takes the value 3
x = ti.Vector([1, 1]) # Error!
- Line 3:
xis an integer because it is assigned an integer value the first time it is declared.
- Line 4:
xis reassigned a floating-point number 3.14 but takes the value 3. This is because 3.14 is automatically cast to integer 3 to match the type of
- Line 5: The system throws an error, because
ti.Vectorcannot be cast into an integer.
ti.types module defines all the supported data types, and they are classified into two categories: primitive types and compound types.
- Primitive types refer to various commonly-used numerical data types, such as
- Compound types refer to various array-like or struct-like data types, including
ti.types.struct. Compound types comprise multiple members of primitive types or of other compound types.
Primitive types refer to scalars, which are the smallest building blocks of compound types. Each primitive type is denoted with a character indicating its category followed by a number indicating its precision bits (number of bits for storing the data). The category can be
i (signed integers),
u (unsigned integers), or
f (floating-point numbers); the precision bits can be
64. Following are the two most commonly used types:
i32: 32-bit signed integer
f32: 32-bit floating-point number.
Not all backends support Taichi's primitive types. See the following table for how a primitive type is supported by various backends. Note that some backends may require extensions to support a specific primitive type.
⭕: Requiring extensions for the backend.
When initializing the Taichi runtime, Taichi automatically uses the following data types as the default primitive data types:
ti.i32: the default integer type.
ti.f32: the default floating-point type.
Taichi allows you to specify the default primitive data type(s) when calling
ti.init(default_ip=ti.i64) # Sets the default integer type to ti.i64
ti.init(default_fp=ti.f64) # Sets the default floating-point type to ti.f64
The numeric literals in the Taichi scope also have default integer/floating-point types. For example, if the default floating-point type is
ti.f32, then a numeric literal
3.14159265358979 in the Taichi scope suffers a precision loss because it is cast to a 32-bit floating-point number, which has a precision of about seven decimal digits.
If you are working on a high-precision application scenario, such as numeric simulation for engineering, set
Taichi supports using
int as the alias for the default integer type and
float as the alias for the default floating-point type. For example, after changing the default primitive types to
f64, you can use
int as the alias for
float as the alias for
x = ti.field(float, 5)
y = ti.field(int, 5)
# Is equivalent to:
x = ti.field(ti.f64, 5)
y = ti.field(ti.i64, 5)
def func(a: float) -> int:
# Is equivalent to:
def func(a: ti.f64) -> ti.i64:
As mentioned at the beginning of this document, the type of a variable in the Taichi scope is statically typed upon initialization. Taichi's compiler performs type checking at compile time, meaning that you cannot change a variable's type once it is initialized. However, from time to time, you may run into situations where you need to switch to a different data type because the original is not feasible for an assignment or calculation. In such situations, you need explicit type casting:
You can use
ti.cast()to convert a value to the target type:
a = 3.14
b = ti.cast(a, ti.i32) # 3
c = ti.cast(b, ti.f32) # 3.0
As of v1.1.0, Taichi allows you to use primitive types such as
ti.i64to convert a scalar variable to a different scalar type:
a = 3.14
x = int(a) # 3
y = float(a) # 3.14
z = ti.i32(a) # 3
w = ti.f64(a) # 3.14
Implicit type casting happens when you accidentally put or assign a value where a different data type is expected.
As a rule of thumb, implicit type casting is a major source of bugs. And Taichi does not recommend resorting to this mechanism.
Implicit type casting can happen in binary operations or in assignments, as explained below.
Taichi implements its own implicit type casting rules for binary operations, which are slightly different from those for the C programming language. In general we have three rules in descending order of priority:
Integer + floating point -> floating point
i32 + f32 -> f32
i16 + f16 -> f16
Low-precision bits + high-precision bits -> high-precision bits
i16 + i32 -> i32
f16 + f32 -> f32
u8 + u16 -> u16
Signed integer + unsigned integer -> unsigned integer
u32 + i32 -> u32
u8 + i8 -> u8
When it comes to rule conflicts, the rule of the highest priority applies:
u8 + i16 -> i16(when rule #2 conflicts with rule #3, rule #2 applies.)
f16 + i32 -> f16(when rule #1 conflicts with rule #2, rule #1 applies.)
A few exceptions:
- bit-shift operations return lhs' (left hand side's) data type:
u8 << i32 -> u8
i16 << i8 -> i16
- Logical operations return
- Comparison operations return
When you assign a value to a variable of a different data type, Taichi implicitly casts the value into that type. Further, if the value is of a higher precision than the variable, a warning of precision loss will be printed.
Example 1: Variable
ais initialized with type
floatand immediately reassigned
1. The reassignment implicitly casts
a = 3.14
a = 1
print(a) # 1.0
Example 2: Variable
ais initialized with type
intand immediately reassigned
3.14. The reassignment implicitly casts
intwith a warning because the type of
intand has a lower precision than
a = 1
a = 3.14
print(a) # 3
Compound types are user-defined data types, which comprise multiple elements. Supported compound types include vectors, matrices, ndarrays, and structs.
Taichi allows you to use all types supplied in the
ti.types module as scaffolds to customize higher-level compound types.
ndarray type is discussed in another document interacting with External Arrays.
You can use the two functions
ti.types.vector() to create your own matrix and vector types:
vec4d = ti.types.vector(4, ti.f64) # a 64-bit floating-point 4D vector type
mat4x3i = ti.types.matrix(4, 3, int) # a 4x3 integer matrix type
You can use these customized types to instantiate vectors and matrices or annotate the data types of function arguments and struct members. For example:
v = vec4d(1, 2, 3, 4) # Create a vector instance, here v = [1.0 2.0 3.0 4.0]
def length(w: vec4d): # vec4d as type hint
You can use the funtion
ti.types.struct() to create a struct type. Try customizing compound types to represent a sphere in the 3D space, which can be abstracted with its center and radius. In the following example, you call
ti.types.struct() to create compound types
sphere_type, respectively. These two types are the higher-level compound types that fit better with your scenario. Subsequently, you can use them as templates to create two instances of spheres (initialize two local variables
# Define a compound type vec3 to represent a sphere's center
vec3 = ti.types.vector(3, float)
# Define a compound type sphere_type to represent a sphere
sphere_type = ti.types.struct(center=vec3, radius=float)
# Initialize sphere1, whose center is at [0,0,0] and whose radius is 1.0
sphere1 = sphere_type(center=vec3([0, 0, 0]), radius=1.0)
# Initialize sphere2, whose center is at [1,1,1] and whose radius is 1.0
sphere2 = sphere_type(center=vec3([1, 1, 1]), radius=1.0)
When a struct contains many members,
ti.types.struct may make your code look messy. Taichi offers a more intuitive way to define a struct: The decorator
@ti.dataclass is a thin wrapper of the struct type:
The code above serves the same purpose as the line below does but provides better readability:
Sphere = ti.types.struct(center=vec3, radius=float)
Another advantage of using
ti.types.struct is that you can define member functions in a dataclass and call them in the Taichi scope, making object-oriented programming (OOP) possible. See the objective data-oriented programming for more information.
Just as you do with any other data type, you can call a compound type directly to create vector, matrix, or struct instances in Taichi.
As of v1.1.0, Taichi supports more options for initializing a struct or a dataclass.
- Pass positional arguments to a struct in the order they are defined.
- Pass keyword arguments to a struct to set the corresponding struct members.
- Unspecified struct members are automatically set to zero.
# The definition above is equivalent to
#Ray = ti.types.struct(ro=vec3, rd=vec3, t=float)
# Use positional arguments to set struct members in order
ray = Ray(vec3(0), vec3(1, 0, 0), 1.0)
# ro is set to vec3(0) and t will be set to 0
ray = Ray(vec3(0), rd=vec3(1, 0, 0))
# both ro and rd are set to vec3(0)
ray = Ray(t=1.0)
# ro is set to vec3(1), rd=vec3(0) and t=0.0
ray = Ray(1)
# All members are set to 0
ray = Ray()
You can create vectors, matrices, and structs using GLSL-like broadcast syntax because their shapes are already known.
For now, the only compound types that support type casting in Taichi are vectors and matrices. Type casting of vectors and matrices is element-wise and results in new vectors and matrices being created:
u = ti.Vector([2.3, 4.7])
v = int(u) # ti.Vector([2, 4])
# If you are using ti.i32 as default_ip, this is equivalent to:
v = ti.cast(u, ti.i32) # ti.Vector([2, 4])