# Get type of structref for function signature

**URL:** <https://numba.discourse.group/t/get-type-of-structref-for-function-signature/1495>\
**Category:** Support: How do I do ...?\
**Created:** [August 11, 2022, 2:05am UTC](https://numba.discourse.group/t/get-type-of-structref-for-function-signature/1495 "2022-08-11T02:05:18Z")\
**Posts on this page:** 10\
**Page:** 1

<div class="post-metadata">

**Author:** ![Alex2262](https://yyz2.discourse-cdn.com/free1/user_avatar/numba.discourse.group/alex2262/32/675_2.png) [@Alex2262](https://numba.discourse.group/u/Alex2262)\
**Post date:** [August 11, 2022, 2:05am UTC](https://numba.discourse.group/t/get-type-of-structref-for-function-signature/1495/1 "2022-08-11T02:05:18Z")

</div>

Basically I have a structref, and a function takes it as an argument and I need the function signature.

I used to use a jitclass for this Position class for my chess engine, but now I’m trying to use a structref instead because jitclasses take too long to JIT compile.

```auto
@structref.register
class PositionStructType(types.StructRef):
    def preprocess_fields(self, fields):
        return tuple((name, types.unliteral(typ)) for name, typ in fields)

class PositionStruct(structref.StructRefProxy):
    def __new__ (cls, board,
                white_pieces,
                black_pieces,
                king_positions,
                castle_ability_bits,
                ep_square, side, hash_key):

        return structref.StructRefProxy. __new__ (cls, board, white_pieces, black_pieces,
            king_positions, castle_ability_bits, ep_square, side, hash_key)

    @property
    def board(self):
        return PositionStruct_get_board(self)

    @property
    def white_pieces(self):
        return PositionStruct_get_white_pieces(self)

    @property
    def black_pieces(self):
        return PositionStruct_get_black_pieces(self)

    @property
    def king_positions(self):
        return PositionStruct_get_king_positions(self)

    @property
    def castle_ability_bits(self):
        return PositionStruct_get_castle_ability_bits(self)

    @property
    def ep_square(self):
        return PositionStruct_get_ep_square(self)

    @property
    def side(self):
        return PositionStruct_get_side(self)

    @property
    def hash_key(self):
        return PositionStruct_get_hash_key(self)

@njit
def PositionStruct_get_board(self):
    return self.board

@njit
def PositionStruct_get_white_pieces(self):
    return self.white_pieces

@njit
def PositionStruct_get_black_pieces(self):
    return self.black_pieces

@njit
def PositionStruct_get_king_positions(self):
    return self.king_positions

@njit
def PositionStruct_get_castle_ability_bits(self):
    return self.castle_ability_bits

@njit
def PositionStruct_get_ep_square(self):
    return self.ep_square

@njit
def PositionStruct_get_side(self):
    return self.side

@njit
def PositionStruct_get_hash_key(self):
    return self.hash_key

structref.define_proxy(PositionStruct, PositionStructType, ["board", "white_pieces", "black_pieces",
                                                            "king_positions", "castle_ability_bits",
                                                            "ep_square", "side", "hash_key"])

@njit
def init_position():
    position = PositionStruct(np.zeros(120, dtype=np.int8),
                              [nb.int64(1) for _ in range(0)], [nb.int64(1) for _ in range(0)],
                              np.zeros(2, dtype=np.uint8), 0, 0, 0, 0)

    return position

```

That above is my structref, and I have a function that takes the position as an argument and needs to return an unsigned 64-bit integer.

```auto
@nb.njit(nb.uint64(Position.class_type.instance_type), cache=True)

```

I used to use this for the function signature, however with the structref this no longer works.

---

<div class="post-metadata">

**Author:** ![nelson2005](https://yyz2.discourse-cdn.com/free1/user_avatar/numba.discourse.group/nelson2005/32/47_2.png) [@nelson2005](https://numba.discourse.group/u/nelson2005)\
**Post date:** [August 11, 2022, 2:31am UTC](https://numba.discourse.group/t/get-type-of-structref-for-function-signature/1495/2 "2022-08-11T02:31:07Z")

</div>

Can you leave the signature definition out of the njit call?

---

<div class="post-metadata">

**Author:** ![Alex2262](https://yyz2.discourse-cdn.com/free1/user_avatar/numba.discourse.group/alex2262/32/675_2.png) [@Alex2262](https://numba.discourse.group/u/Alex2262)\
**Post date:** [August 11, 2022, 2:32am UTC](https://numba.discourse.group/t/get-type-of-structref-for-function-signature/1495/3 "2022-08-11T02:32:48Z")

</div>

I want to return a uint64, and in the future I might try to do ahead of time compilation. I guess I could leave it out, but it would be better if I can use it.

---

<div class="post-metadata">

**Author:** ![nelson2005](https://yyz2.discourse-cdn.com/free1/user_avatar/numba.discourse.group/nelson2005/32/47_2.png) [@nelson2005](https://numba.discourse.group/u/nelson2005)\
**Post date:** [August 11, 2022, 2:39am UTC](https://numba.discourse.group/t/get-type-of-structref-for-function-signature/1495/4 "2022-08-11T02:39:18Z")

</div>

Can you post a minimal complete running example without the signature?

---

<div class="post-metadata">

**Author:** ![Alex2262](https://yyz2.discourse-cdn.com/free1/user_avatar/numba.discourse.group/alex2262/32/675_2.png) [@Alex2262](https://numba.discourse.group/u/Alex2262)\
**Post date:** [August 11, 2022, 2:46am UTC](https://numba.discourse.group/t/get-type-of-structref-for-function-signature/1495/5 "2022-08-11T02:46:24Z")

</div>

This is the function, which returns a uint64 hash key. Without the function signature it doesn’t run correctly.

```auto
@nb.njit(nb.uint64(Position.class_type.instance_type), cache=True)
def compute_hash(position):
    code = 0

    for i in range(64):
        pos = STANDARD_TO_MAILBOX[i]
        if position.board[pos] > BLACK_KING:
            continue

        code ^= PIECE_HASH_KEYS[position.board[pos]][i]

    if position.ep_square:
        code ^= EP_HASH_KEYS[MAILBOX_TO_STANDARD[position.ep_square]]

    code ^= CASTLE_HASH_KEYS[position.castle_ability_bits]

    if position.side: # side 1 is black, 0 is white
        code ^= SIDE_HASH_KEY

    return code

```

These are the constants used in the code

```auto
PIECE_HASH_KEYS = np.random.randint(1, 2**64 - 1, size=(12, 64), dtype=np.uint64)
EP_HASH_KEYS = np.random.randint(1, 2**64 - 1, size=64, dtype=np.uint64)
CASTLE_HASH_KEYS = np.random.randint(1, 2 ** 64 - 1, size=16, dtype=np.uint64)
SIDE_HASH_KEY = np.random.randint(1, 2 ** 64 - 1, dtype=np.uint64)

```

---

<div class="post-metadata">

**Author:** ![Alex2262](https://yyz2.discourse-cdn.com/free1/user_avatar/numba.discourse.group/alex2262/32/675_2.png) [@Alex2262](https://numba.discourse.group/u/Alex2262)\
**Post date:** [August 11, 2022, 2:52am UTC](https://numba.discourse.group/t/get-type-of-structref-for-function-signature/1495/6 "2022-08-11T02:52:44Z")

</div>

I tested, without the function signature it does work. But if I wanted to ahead of time compile it in the future then I guess I would need it, but I’m not sure if it’s possible to get the type of a structref.

---

<div class="post-metadata">

**Author:** ![nelson2005](https://yyz2.discourse-cdn.com/free1/user_avatar/numba.discourse.group/nelson2005/32/47_2.png) [@nelson2005](https://numba.discourse.group/u/nelson2005)\
**Post date:** [August 11, 2022, 2:57am UTC](https://numba.discourse.group/t/get-type-of-structref-for-function-signature/1495/7 "2022-08-11T02:57:46Z")

</div>

Can you call it once without the signature and then print the signature of the jitted function?

---

<div class="post-metadata">

**Author:** ![Alex2262](https://yyz2.discourse-cdn.com/free1/user_avatar/numba.discourse.group/alex2262/32/675_2.png) [@Alex2262](https://numba.discourse.group/u/Alex2262)\
**Post date:** [August 11, 2022, 2:59am UTC](https://numba.discourse.group/t/get-type-of-structref-for-function-signature/1495/8 "2022-08-11T02:59:41Z")

</div>

How do I print the signature of the function?

---

<div class="post-metadata">

**Author:** ![mgirardis](https://yyz2.discourse-cdn.com/free1/user_avatar/numba.discourse.group/mgirardis/32/1205_2.png) [@mgirardis](https://numba.discourse.group/u/mgirardis)\
**Post date:** [March 8, 2025, 6:32pm UTC](https://numba.discourse.group/t/get-type-of-structref-for-function-signature/1495/9 "2025-03-08T18:32:04Z")

</div>

For reference, here is the way to get the type signature of a structref. You first create an instance of it and then inspect its type using `typeof()`. In Numba, structured references (`structref.StructRef`) have their types registered in the `types` module.

Basically, in your example, before defining the `init_position()` function, you need

```python
from numba import typeof,njit,types

_position_type = typeof(PositionStruct(np.zeros(120, dtype=np.int8),
                              [nb.int64(1) for _ in range(0)], [nb.int64(1) for _ in range(0)],
                              np.zeros(2, dtype=np.uint8), 0, 0, 0, 0))

@njit(_position_type(types.void))
def init_position():
    position = PositionStruct(np.zeros(120, dtype=np.int8),
                              [nb.int64(1) for _ in range(0)], [nb.int64(1) for _ in range(0)],
                              np.zeros(2, dtype=np.uint8), 0, 0, 0, 0)

    return position

```

Below, there’s a complete example where I needed to do something just like you needed with your `Position` struct.

### Steps to obtain the type signature:

1. **Create an instance** of `NeuronRandNetParamtruct`.
2. **Use `numba.typeof()`** to obtain the corresponding Numba type.
3. **Use it in your function signature**.

* * *

### Solution:

#### 1. Obtain the type signature

```python
from numba import typeof, njit

# defining the structref
@structref.register
class NeuronRandNetParamtructType(types.StructRef):
    def preprocess_fields(self, fields):
        return tuple((name, types.unliteral(typ)) for name, typ in fields)

class NeuronRandNetParamtruct(structref.StructRefProxy):
    def __new__ (cls,Iext,mu,theta,Gamma,I,P_poisson,tauTinv,uT):
        # Overriding the __new__ method is optional, doing so
        # allows Python code to use keyword arguments,
        # or add other customized behavior.
        # The default __new__ takes `*args`.
        # IMPORTANT: Users should not override __init__.
        return structref.StructRefProxy. __new__ (cls,Iext,mu,theta,Gamma,I,P_poisson,tauTinv,uT)
    pass

structref.define_proxy(NeuronRandNetParamtruct, NeuronRandNetParamtructType, ['Iext','mu','theta','Gamma','I','P_poisson','tauTinv','uT'])

# Create an instance of NeuronRandNetParamtruct
par_instance = NeuronRandNetParamtruct(0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0)

# Get its type
_neuronRandNetParamStruct_signature = typeof(par_instance)

```

#### 2. Use the obtained type in function signature

```python
@njit(types.Tuple((types.float64, types.float64, types.float64, types.float64))(
    types.float64, types.float64, types.float64, _neuronRandNetParamStruct_signature
))
def GLNetEIRand_adaptthresh_iter(V, X, synapticInput, par):
    par.theta = par.theta * (1.0 - par.tauTinv + par.uT * X)
    V = (par.mu * V + par.I + par.Iext + synapticInput) * (1.0 - X)
    X = bool2float(random.random() < (PHI(V, par.theta, par.Gamma) * (1.0 - par.P_poisson) + par.P_poisson))
    return V, X, par.theta, par.P_poisson

```

Now `_neuronRandNetParamStruct_signature` contains the correct Numba type for your `NeuronRandNetParamtruct` structure, allowing you to use it in the function signature.

---

<div class="post-metadata">

**Author:** ![nelson2005](https://yyz2.discourse-cdn.com/free1/user_avatar/numba.discourse.group/nelson2005/32/47_2.png) [@nelson2005](https://numba.discourse.group/u/nelson2005)\
**Post date:** [March 9, 2025, 4:21pm UTC](https://numba.discourse.group/t/get-type-of-structref-for-function-signature/1495/10 "2025-03-09T16:21:11Z")

</div>

“In most cases you don’t have to specify types. Numba will determine them the first time you call the function. If you are interested in the types you can call my\_funct.nopython\_signatures to see what was detected. –  
max9111  
CommentedFeb 15, 2021 at 12:22”  
[python 3.x - how to define multiple signatures for a function in numba - Stack Overflow](https://stackoverflow.com/questions/66205186/how-to-define-multiple-signatures-for-a-function-in-numba#:~:text=In%20most%20cases,at%2012%3A22)