What does the struct function do in MATLAB / RunMat?

S = struct(...) creates scalar structs or struct arrays by pairing field names with values. The inputs can be simple name/value pairs, existing structs, or cell arrays whose elements are expanded into struct array entries.

How does the struct function behave in MATLAB / RunMat?

• Field names must satisfy the MATLAB isvarname rules: they start with a letter or underscore and contain only letters, digits, or underscores.
• The last occurrence of a repeated field name wins and overwrites earlier values.
• String scalars, character vectors, and single-element string arrays are accepted as field names.
• struct() returns a scalar struct with no fields, while struct([]) yields a 0×0 struct array.
• When any value input is a cell array, every cell array input must share the same size. Non-cell inputs are replicated across every element of the resulting struct array.
• Passing an existing struct or struct array (struct(S)) creates a deep copy; the original data is untouched.

struct Function GPU Execution Behaviour

struct performs all bookkeeping on the host. GPU-resident values—such as tensors created with gpuArray—are stored as-is inside the resulting struct or struct array. No kernels are launched and no data is implicitly gathered back to the CPU.

GPU residency in RunMat (Do I need gpuArray?)

Usually not. RunMat's planner keeps GPU values resident as long as downstream operations can profit from them. You can still seed GPU residency explicitly with gpuArray for MATLAB compatibility; the handles remain untouched inside the struct until another builtin decides to gather or operate on them.

Examples

Creating a simple structure for named fields

s = struct("name", "Ada", "score", 42);
disp(s.name);
disp(s.score);

Expected output:

Ada
    42

Building a struct array from paired cell inputs

names = {"Ada", "Grace"};
ages = {36, 45};
people = struct("name", names, "age", ages);
{people.name}

Expected output:

    {'Ada'}    {'Grace'}

Broadcasting scalars across a struct array

ids = struct("id", {101, 102, 103}, "department", "Research");
{ids.department}

Expected output:

    {'Research'}    {'Research'}    {'Research'}

Copying an existing structure

a = struct("id", 7, "label", "demo");
b = struct(a);
b.id = 8;
disp([a.id b.id]);

Expected output:

     7     8

Building an empty struct array

s = struct([]);
disp(size(s));

Expected output:

     0     0

FAQ

Do field names have to be valid identifiers?

Yes. RunMat mirrors MATLAB and requires names to satisfy isvarname. Names must begin with a letter or underscore and may contain letters, digits, and underscores.

How do I create a struct array?

Provide one or more value arguments as cell arrays with identical sizes. Each cell contributes the value for the corresponding struct element. Non-cell values are replicated across all elements.

What happens when the same field name appears more than once?

The last value wins; earlier values for the same field are overwritten.

Does struct gather GPU data back to the CPU?

No. GPU tensors remain device-resident handles inside the resulting struct or struct array.

Can I pass non-string objects as field names?

No. Field names must be provided as string scalars, character vectors, or single-element string arrays. Passing other types raises an error.

See Also

load, whos, gpuArray, gather