# Generate function code
**URL:** https://discourse.julialang.org/t/generate-function-code/67385
**Category:** General Usage
**Tags:** metaprogramming
**Created:** [August 30, 2021, 11:40pm UTC](https://discourse.julialang.org/t/generate-function-code/67385 "2021-08-30T23:40:20Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@andrey2185](https://discourse.julialang.org/u/andrey2185)
#### Post date: [August 30, 2021, 11:40pm UTC](https://discourse.julialang.org/t/generate-function-code/67385/1 "2021-08-30T23:40:20Z")
Hellow!
I have
```julia
type_list = [
# type code
#
Int64 0x11;
Int32 0xa2;
Int16 0x33;
Int8 0x24;
#
UInt64 0x15;
UInt32 0xb6;
UInt16 0x7a;
UInt8 0x8f;
#
Float64 0x92;
Float32 0x0a;
Float16 0x0b;
]
```
I need:
```julia
function get_type_by_code(code::UInt8)
code == 0x11 && return Int64
code == 0xa2 && return Int32
code == 0x33 && return Int16
code == 0x24 && return Int8
code == 0x15 && return UInt64
code == 0xb6 && return UInt32
code == 0x7a && return UInt16
code == 0x8f && return UInt8
code == 0x92 && return Float64
code == 0x0a && return Float32
code == 0x0b && return Float16
end
```
I do:
```julia
code_string = "function get_type_by_code(code::UInt8)\n"
for i = 1 : length(type_list[:,1])
code_string *= " code == $(type_list[i,2]) && return $(type_list[i,1])\n"
end
code_string *= "end"
Base.include_string(Main, code_string)
```
how to make it better?
---
### Author:  [@tomerarnon](https://discourse.julialang.org/u/tomerarnon)
#### Post date: [August 31, 2021, 1:38am UTC](https://discourse.julialang.org/t/generate-function-code/67385/2 "2021-08-31T01:38:15Z")
Firstly, you should use a Dict rather than a Matrix. Once you do, is this good enough?
```julia
get_type_by_code(code) = type_list[code]
```
---
### Author:  [@jling](https://discourse.julialang.org/u/jling)
#### Post date: [August 31, 2021, 1:41am UTC](https://discourse.julialang.org/t/generate-function-code/67385/3 "2021-08-31T01:41:00Z")
```julia
const type_list = Dict(
0x11 => Int64,
0xa2 => Int32,
0x33 => Int16,
0x24 => Int8,
0x15 => UInt64,
0xb6 => UInt32,
0x7a => UInt16,
0x8f => UInt8,
0x92 => Float64,
0x0a => Float32,
0x0b => Float16,
)
```
and then just `type_list[0x11]` to get `Int64`
---
### Author:  [@andrey2185](https://discourse.julialang.org/u/andrey2185)
#### Post date: [August 31, 2021, 8:16am UTC](https://discourse.julialang.org/t/generate-function-code/67385/4 "2021-08-31T08:16:25Z")
No, i need exactly this function by example:
```julia
function get_type_by_code(code::UInt8)
code == 0x11 && return Int64
code == 0xa2 && return Int32
code == 0x33 && return Int16
code == 0x24 && return Int8
code == 0x15 && return UInt64
code == 0xb6 && return UInt32
code == 0x7a && return UInt16
code == 0x8f && return UInt8
code == 0x92 && return Float64
code == 0x0a && return Float32
code == 0x0b && return Float16
end
```
```julia
const type_list2 = Dict(
0x11 => Int64,
0xa2 => Int32,
0x33 => Int16,
0x24 => Int8,
0x15 => UInt64,
0xb6 => UInt32,
0x7a => UInt16,
0x8f => UInt8,
0x92 => Float64,
0x0a => Float32,
0x0b => Float16,
)
using BenchmarkTools
@btime type_list2[0x92] # 1.900 ns (0 allocations: 0 bytes)
@btime get_type_by_code(0x92) # 0.001 ns (0 allocations: 0 bytes)
```
this is done for convenience and speed, the function is not one,
I edit only main list, then code generation
---
### Author:  [@andrey2185](https://discourse.julialang.org/u/andrey2185)
#### Post date: [August 31, 2021, 8:18am UTC](https://discourse.julialang.org/t/generate-function-code/67385/5 "2021-08-31T08:18:21Z")
Я делаю:
```julia
code_string = "function get_type_by_code(code::UInt8)\n"
for i = 1 : length(type_list[:,1])
code_string *= " code == $(type_list[i,2]) && return $(type_list[i,1])\n"
end
code_string *= "end"
Base.include_string(Main, code_string)
```
как сделать лучше?
---
### Author:  [@tomerarnon](https://discourse.julialang.org/u/tomerarnon)
#### Post date: [August 31, 2021, 9:55pm UTC](https://discourse.julialang.org/t/generate-function-code/67385/6 "2021-08-31T21:55:55Z")
> [@andrey2185](#):
>
> ```julia
> @btime type_list2[0x92] # 1.900 ns (0 allocations: 0 bytes)
> @btime get_type_by_code(0x92) # 0.001 ns (0 allocations: 0 bytes)
>
> ```
There’s no such thing as pico-second function evaluations (this is a common confusion, and the result of constant propagation in the compiler). Using the `Ref` trick from the `BenchmarkTools` docs, and placing the Dict into a function for similar effect, we see they’re much more similar than that:
```julia
julia> get_type_by_code_dict(x) = type_list2[x];
julia> @btime get_type_by_code_dict($(Ref(0x92))[])
6.828 ns (0 allocations: 0 bytes)
Float64
julia> @btime get_type_by_code($(Ref(0x92))[])
3.266 ns (0 allocations: 0 bytes)
Float64
```
You can use a Base.ImmutableDict to regain that speed in this case:
```julia
julia> const type_list_imm = Base.ImmutableDict(
0x11 => Int64,
0xa2 => Int32,
0x33 => Int16,
0x24 => Int8,
0x15 => UInt64,
0xb6 => UInt32,
0x7a => UInt16,
0x8f => UInt8,
0x92 => Float64,
0x0a => Float32,
0x0b => Float16,
);
julia> get_type_by_code_imdict(x) = type_list_imm[x];
julia> @btime get_type_by_code_imdict($(Ref(0x92))[])
3.292 ns (0 allocations: 0 bytes)
Float64
julia> @btime get_type_by_code($(Ref(0x92))[])
3.268 ns (0 allocations: 0 bytes)
Float64
```
That said, if you really want to create such a function from your `Dict`, you should not use strings but rather `Expr`s (expressions). The Metaprogramming section of the julia manual is a great place to start learning how to do this.
---
### Author:  [@serhii](https://discourse.julialang.org/u/serhii)
#### Post date: [January 27, 2022, 9:31pm UTC](https://discourse.julialang.org/t/generate-function-code/67385/7 "2022-01-27T21:31:34Z")
How about value [types](https://docs.julialang.org/en/v1/manual/types/#%22Value-types%22)? One essentially can do pattern matching with them just by using multiple dispatch feature.