struct — Create scalar structs or struct arrays from field/value inputs with MATLAB-compatible construction rules.

S = struct(...) creates scalar structs or struct arrays by pairing field names with values. It supports MATLAB-compatible name/value, struct-copy, and cell-expansion construction forms.

Syntax

S = struct()
S = struct(template)
S = struct(field, value, ...)

Inputs

Returns

Errors

How struct works

• Field names must satisfy the MATLAB isvarname rules: they start with a letter, contain only letters, digits, or underscores, stay within namelengthmax, and are not MATLAB keywords.
• 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.
• Numeric field values retain their exact class, shape, and storage. GPU-resident field values remain resident handles rather than being gathered during construction.
• Passing an existing struct or struct array (struct(S)) creates a deep copy; the original data is untouched.

Does RunMat run struct on the GPU?

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 memory and residency

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

Using struct with coding agents

Open a RunMat example with live inputs, then ask the agent to explain how struct changes the result.

FAQ

Related Structs functions

Open-source implementation

Unlike proprietary runtimes, every RunMat function is open-source. Read exactly how struct is executed, line by line, in Rust.

• View the source for struct in Rust on GitHub
• Learn how the RunMat runtime works
• Found a bug? Open an issue with a minimal reproduction.

About RunMat

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