# String Argument in CUDA Signature

**URL:** <https://numba.discourse.group/t/string-argument-in-cuda-signature/1395>\
**Category:** Support: How do I do ...?\
**Created:** [June 18, 2022, 10:40pm UTC](https://numba.discourse.group/t/string-argument-in-cuda-signature/1395 "2022-06-18T22:40:52Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![seanlaw](https://yyz2.discourse-cdn.com/free1/user_avatar/numba.discourse.group/seanlaw/32/506_2.png) [@seanlaw](https://numba.discourse.group/u/seanlaw)\
**Post date:** [June 18, 2022, 10:40pm UTC](https://numba.discourse.group/t/string-argument-in-cuda-signature/1395/1 "2022-06-18T22:40:52Z")

</div>

The Numba documentation provides details regarding the [types and signatures](https://numba.readthedocs.io/en/stable/reference/types.html?highlight=cuda%20signature) that are supported. For CUDA, it is common to declare a function that accepts numbers, arrays, and booleans with something like:

```auto
@cuda.jit(
    "(i8, f8, f8[:], i8[:], b1)"
)
def some_func(some_int, some_float, some_float_array, some_int_array, some_bool):

```

I was wondering if it is possible specify a string? Let’s say for a CUDA kernel that accepts an argument like:

```auto
# add CUDA signature here
def some_func(side="left"):
    if side == "left":
        # do something
    if side == "right":
        # do something else

```

I know this can be done for `@njit` but it wasn’t clear if this were possible in CUDA

---

<div class="post-metadata">

**Author:** ![gmarkall](https://yyz2.discourse-cdn.com/free1/user_avatar/numba.discourse.group/gmarkall/32/42_2.png) [@gmarkall](https://numba.discourse.group/u/gmarkall)\
**Post date:** [June 26, 2022, 4:15pm UTC](https://numba.discourse.group/t/string-argument-in-cuda-signature/1395/2 "2022-06-26T16:15:44Z")

</div>

Unfortunately not - trying to compile something that accepts a string:

```python
from numba import cuda

@cuda.jit('void(int32[::1], unicode_type)')
def f(x, s):
    if s == 'left':
        r = 1
    elif s == 'right':
        r = 2
    else:
        r = 3
    x[0] = r

```

results in an error:

```auto
NotImplementedError: No definition for lowering <built-in method eq_impl of _dynfunc._Closure object at 0x7fe2cfe0b160>(unicode_type, unicode_type) -> bool

```

(this error message is a bug though, a `NotImplementedError` shouldn’t be thrown from lowering)

---

<div class="post-metadata">

**Author:** ![seanlaw](https://yyz2.discourse-cdn.com/free1/user_avatar/numba.discourse.group/seanlaw/32/506_2.png) [@seanlaw](https://numba.discourse.group/u/seanlaw)\
**Post date:** [June 26, 2022, 5:28pm UTC](https://numba.discourse.group/t/string-argument-in-cuda-signature/1395/3 "2022-06-26T17:28:04Z")

</div>

Thank you @gmarkall! Would it be any different if it were a device function instead (i.e., a kernel that calls this function)?

```auto
@cuda.jit(device=True)
def f(x, s):
    if s == 'left':
        r = 1
    elif s == 'right':
        r = 2
    else:
        r = 3
    x[0] = r

```

Or would this also fall into the same fate? I guess there would also be no way to set a kernel variable to a string?

---

<div class="post-metadata">

**Author:** ![gmarkall](https://yyz2.discourse-cdn.com/free1/user_avatar/numba.discourse.group/gmarkall/32/42_2.png) [@gmarkall](https://numba.discourse.group/u/gmarkall)\
**Post date:** [June 27, 2022, 10:08am UTC](https://numba.discourse.group/t/string-argument-in-cuda-signature/1395/4 "2022-06-27T10:08:41Z")

</div>

It would fall into the same fate - the error appeared due to a lack of support for comparing strings in CUDA.

For this use case, could an Enum class work instead? E.g.

```python
import numpy as np
from numba import cuda
from enum import Enum

class Hand(Enum):
    LEFT = 1
    RIGHT = 2
    OTHER = 3

@cuda.jit()
def f(x, s):
    if s == Hand.LEFT:
        r = 7
    elif s == Hand.RIGHT:
        r = 31
    else:
        r = -1
    x[0] = r

x = cuda.device_array(1, np.int32)
f[1, 1](x, Hand.RIGHT)

print(x[0])
np.testing.assert_equal(x[0], 31)

```

runs and prints `31`.

---

<div class="post-metadata">

**Author:** ![seanlaw](https://yyz2.discourse-cdn.com/free1/user_avatar/numba.discourse.group/seanlaw/32/506_2.png) [@seanlaw](https://numba.discourse.group/u/seanlaw)\
**Post date:** [June 27, 2022, 1:01pm UTC](https://numba.discourse.group/t/string-argument-in-cuda-signature/1395/5 "2022-06-27T13:01:51Z")

</div>

Thank you! I will play with your suggestion